PROSPECTUS SUPPLEMENT SUMMARY

The following summary contains basic information about us and our securities. It is not complete and may not contain all of the information you may want to consider. You should review the more detailed information contained in this prospectus supplement and in the accompanying prospectus and in the statement of additional information, especially the information set forth under the heading “Risk Factors” beginning on page 31 of the accompanying prospectus.

The Fund

The Fund is a diversified, closed-end management investment company, with total managed assets of $1.14 billion as of March 31, 2016. We commenced operations in June 2002 following our initial public offering. Our investment objective is to provide total return through a combination of capital appreciation and current income.

Investment Adviser

Calamos Advisors LLC (the “Adviser” or “Calamos”) serves as our investment adviser. Calamos is responsible on a day-to-day basis for investment of the Fund’s portfolio in accordance with its investment objective and policies. Calamos makes all investment decisions for the Fund and places purchase and sale orders for the Fund’s portfolio securities. As of March 31, 2016, Calamos managed approximately $21.0 billion in assets of individuals and institutions. Calamos is a wholly-owned subsidiary of Calamos Investments LLC and an indirect subsidiary of Calamos Asset Management, Inc., a publicly traded holding company.

The Fund pays Calamos an annual fee, payable monthly, for its investment management services equal to 0.80% of the Fund’s average weekly managed assets. “Managed assets” means the total assets of the Fund (including any assets attributable to any leverage that may be outstanding) minus the sum of liabilities (other than debt representing financial leverage). See “Management of the Fund” on page 40 of the accompanying prospectus.

The principal business address of the Adviser is 2020 Calamos Court, Naperville, Illinois 60563.

The Offering

The Fund and Calamos entered into the Sales Agreement with JonesTrading Institutional Services LLC (“JonesTrading”) relating to the common shares offered by this prospectus supplement and the accompanying prospectus. In accordance with the terms of the Sales Agreement, we may offer and sell up to 6,232,167 of our common shares, no par value per share, from time to time through JonesTrading as our agent for the offer and sale of the common shares. As of March 31, 2016, the Fund had offered and sold 3,767,833 common shares pursuant to prior sales agreements with JonesTrading, resulting in proceeds (net of all fees, expenses and commissions) of $42,792,625. The prior sales agreement with JonesTrading has been terminated.

Our common shares are listed on the NASDAQ Global Select Market (“NASDAQ”) under the symbol “CHY.” As of March 31, 2016, the last reported sale price for our common shares was $10.39.

Sales of our common shares, if any, under this prospectus supplement and the accompanying prospectus may be made in negotiated transactions or transactions that are deemed to be “at the market” as defined in Rule 415 under the 1933 Act, including sales made directly on the NASDAQ or sales made to or through a market maker other than on an exchange. See “Plan of Distribution” in this prospectus supplement. Our common shares may not be sold through agents, underwriters or dealers without delivery or deemed delivery of a prospectus and a prospectus supplement describing the method and terms of the offering of our securities. Under the 1940 Act, the Fund may not sell any common shares at a price below the current net asset value of such common shares, exclusive of any distributing commission or discount.

Use of Proceeds

Unless otherwise specified in this prospectus supplement, we currently intend to use the net proceeds from the sale of our common shares in this offering primarily to invest in accordance with our investment objective and policies (as described under “Investment Objective and Principal Investment Strategies,” beginning on page 19 of the accompanying prospectus) within approximately three months of receipt of such proceeds. We may also use proceeds from the sale of our securities to retire all or a portion of any short-term debt within approximately three months, and for working capital purposes, including the payment of interest and operating expenses, although there is currently no intent to issue securities primarily for this purpose. The combined interest rate charged under the BNP Agreement and the SSB Agreement as of March 31, 2016 was 1.23%. Reduction of the leverage employed by the Fund will reduce our assets available for investment, and may have a negative impact on the Fund. See “Leverage,” beginning on page 25 of the accompanying prospectus, and “Risk Factors — Additional Risks to Common Shareholders — Reduction of Leverage Risk” on page 38 — of the accompanying prospectus.

PROSPECTUS SUMMARY

The following summary contains basic information about us and our securities. It is not complete and may not contain all of the information you may want to consider. You should review the more detailed information contained in this prospectus and in any related prospectus supplement and in the statement of additional information, especially the information set forth under the heading “Risk Factors” beginning on page 31 of this prospectus.

The Fund

The Fund is a diversified, closed-end management investment company. We commenced operations in May 2003 following our initial public offering. As of January 31, 2016, we had $1.1 billion of total managed assets and $362 million of outstanding borrowings under a Committed Facility Agreement and a Credit Agreement, each as described below, with no additional structural leverage. Structural leverage refers to borrowings under the Credit Agreement in respect of which the Fund’s interest payments are reduced or eliminated by the Fund’s securities lending activities. Our fiscal year ends on October 31. Our investment objective is to provide total return through a combination of capital appreciation and current income.

Investment Adviser

Calamos Advisors LLC (the “Adviser” or “Calamos”) serves as our investment adviser. Calamos is responsible on a day-to-day basis for investment of the Fund’s portfolio in accordance with its investment objective and policies. Calamos makes all investment decisions for the Fund and places purchase and sale orders for the Fund’s portfolio securities. As of October 31, 2015, Calamos managed approximately $23.0 billion in assets of individuals and institutions. Calamos is a wholly-owned subsidiary of Calamos Investments LLC (“CILLC”) and an indirect subsidiary of Calamos Asset Management, Inc., a publicly traded holding company.

The Fund pays Calamos an annual fee, payable monthly, for its investment management services equal to 0.80% of the Fund’s average weekly managed assets. “Managed assets” means the total assets of the Fund (including any assets attributable to any leverage that may be outstanding) minus the sum of liabilities (other than debt representing financial leverage). “Net assets” does not include any assets attributable to any leverage that may be outstanding. See “Management of the Fund.”

The principal business address of the Adviser is 2020 Calamos Court, Naperville, Illinois 60563.

The Offering

We may offer, on an immediate, continuous or delayed basis, up to $100,000,000 of our securities on terms to be determined at the time of the offering. Our common shares will be offered at prices at or above net asset value (often referred to as “NAV”) and on terms to be set forth in one or more prospectus supplements to the prospectus. To the extent that the Fund issues common shares and current shareholders do not participate, those current shareholders may experience a dilution of their voting rights as new shares are issued to the public. Depending on the facts, any issuance of new common shares may also have the effect of reducing any premium to per share net asset value at which the shares might trade and the market price at which the shares might trade.

Currently, the Fund has not determined the timing of any preferred shares or debt offering. Preferred shares and debt securities (collectively, “senior securities”) may be auction rate securities, in which case the senior securities will not be listed on any exchange or automated quotation system. Rather, investors generally may only buy and sell auction rate securities through an auction conducted by an auction agent and participating broker-dealers.

We may offer our securities directly to one or more purchasers, through agents that we or they designate from time to time, or to or through underwriters or dealers. The prospectus supplement relating to the offering will identify any agents or underwriters involved in the sale of our securities, and will set forth any applicable purchase price, fee, commission or discount arrangement between us and such agents or underwriters or among underwriters or the basis upon which such amount may be calculated. See “Plan of Distribution.” Our securities may not be sold through agents, underwriters or dealers without delivery or deemed delivery of a prospectus and prospectus supplement describing the method and terms of the offering of our securities.

Use of Proceeds

Unless otherwise specified in a prospectus supplement, we currently intend to use the net proceeds from the sale of our securities primarily to invest in accordance with our investment objective and policies within approximately three months of receipt of such proceeds. We may also use proceeds from the sale of our securities to (i) retire all or a portion of any short-term debt we incur in pursuit of our investment objective and policies, (ii) redeem any outstanding senior securities, and (iii) for working capital purposes, including the payment of interest and operating expenses, although there is currently no intent to issue securities primarily for these purposes.

Dividends and Distributions on Common Shares

The Fund currently intends to make monthly distributions to common shareholders at a level rate established by the Board of Trustees. The rate may be modified by the Board of Trustees from time to time. Monthly distributions may include net investment income, net realized short-term capital gain and, if necessary to maintain a level distribution, return of capital. The Fund may at times in its discretion pay out less than the entire amount of net investment income earned in any particular period and may at times pay out such accumulated undistributed income in addition to net investment income earned in other periods in order to permit the Fund to maintain a more stable level of distributions. As a result, the distributions paid by the Fund to holders of common shares for any particular period may be more or less than the amount of net investment income earned by the Fund during such period. Net realized short-term capital gains distributed to shareholders will be taxed as ordinary income for federal income tax purposes. Generally, there may be at least one additional distribution per calendar year that may include net realized long-term capital gain (if any), which will be taxed for federal income tax purposes at long-term capital gain rates. To the extent the Fund distributes an amount in excess of the Fund’s current and accumulated earnings and profits, such excess, if any, will be treated by a shareholder for federal income tax purposes as a tax-free return of capital to the extent of the shareholder’s adjusted tax basis in his, her or its shares and thereafter as a gain from the sale or exchange of such shares. Any such distributions made by the Fund will reduce the shareholder’s adjusted tax basis in his, her or its shares to the extent that the distribution constitutes a return of capital on a tax basis during any calendar year and, thus, could potentially subject the shareholder to capital gains taxation in connection with a later sale of Fund shares, even if those shares are sold at a price that is lower than the shareholder’s original investment price. To the extent that the Fund’s distributions exceed the Fund’s current and accumulated earnings and profits, the distribution payout rate will exceed the yield generated from the Fund’s investments. There is no guarantee that the Fund will realize capital gain in any given year. Distributions are subject to re-characterization for federal income tax purposes after the end of the fiscal year.

The Fund has made regular monthly distributions to its common shareholders of $0.1219 per share from August 2003 through October 2008, and monthly distributions of $0.0850 from November 2008 through March 2014 and $0.10 since April 2014. Additionally, the Fund has made special supplemental distributions, in addition to the regular monthly distributions, of $0.0920, $0.0232, and $0.1052 in January 2006, January 2007, and January 2008, respectively. The Fund intends to distribute to common shareholders all or a portion of its net investment income monthly and net realized capital gains, if any, at least annually. The sources of these distributions have varied over time and will continue to do so. The sources of these distributions may include net investment income, capital gain and return of capital.

On November 4, 2008, the Commission granted Calamos, on behalf of itself and certain funds that it manages, including the Fund, an order granting an exemption from Section 19(b) of, and Rule 19b-1 under, the Investment Company Act of 1940, as amended (the “1940 Act”) to conditionally permit the Fund to make periodic distributions of long-term capital gains with respect to the Fund’s outstanding common stock as frequently as twelve times each year, so long as the Fund complies with the conditions of the order and maintains in effect a distribution policy with respect to the Fund’s common shares calling for periodic distributions of an amount equal to a fixed amount per share, a fixed percentage of market price per share or a fixed percentage of the Fund’s net asset value per share (a “Managed Dividend Policy”).

The relief described above will expire on the effective date of any amendment to Rule 19b-1 under the 1940 Act that provides relief permitting certain closed-end investment companies to make periodic distributions of long-term capital gains with respect to their outstanding common stock as frequently as twelve times each year. As a result of the granting of the order, the Fund may implement a Managed Dividend Policy, although it has not done so as of the date of this prospectus. Under a Managed Dividend Policy, if, for any distribution, undistributed net investment income and net realized capital gains were less than the amount of the distribution, the difference would be distributed from the Fund’s other assets. In addition, in order to make such distributions, the Fund might have to sell a portion of its investment portfolio at a time when independent investment judgment might not dictate such action. Notwithstanding receipt of the exemptive relief, currently the Fund does not intend to implement a Managed Dividend Policy until such time as its implementation is in the best interests of the Fund and our shareholders. In addition, it is not contemplated that we will change the terms of our current level distribution policy, which otherwise meets the requirements of Section 19 of the 1940 Act, in connection with any future implementation of the managed distribution order. For more information about the Managed Dividend Policy see “Dividends and Distributions on Common Shares.”

Pursuant to the Fund’s Automatic Dividend Reinvestment Plan, unless a shareholder is ineligible or elects otherwise, all dividends and capital gain distributions on common shares are automatically reinvested in additional common shares of the Fund. However, an investor can choose to receive dividends and distributions in cash. Since investors can participate in the automatic dividend reinvestment plan only if their broker or nominee participates in our plan, you should contact your broker or nominee to confirm that you are eligible to participate in the plan. See “Dividends and Distributions; Automatic Dividend Reinvestment Plan.”

Investment Policies

Primary Investments.    Under normal circumstances, the Fund invests at least 80% of its managed assets in a diversified portfolio of convertible securities and below investment grade (high yield/high risk) non-convertible debt securities. The portion of the Fund’s assets invested in convertible securities and below investment grade (high yield/high risk) non-convertible debt securities will vary from time to time consistent with the Fund’s investment objective, changes in equity prices and changes in interest rates and other economic and market factors, although, under normal circumstances, the Fund will invest at least 20% of its managed assets in convertible securities and at least 20% of its managed assets in below investment grade (high yield/high risk) non-convertible debt securities (so long as, under normal circumstances, the combined total equals at least 80% of the Fund’s managed assets). The Fund invests in securities with a broad range of maturities. The average term to maturity of the Fund’s securities typically will range from five to ten years. See “Investment Objective and Principal Investment Strategies — Principal Investment Strategies.”

The Fund’s derivative activities are principally focused on the following derivatives: interest rate swaps, convertible securities, synthetic convertible securities, options on individual securities, index options and forward currency exchange contracts. However, the Fund reserves the right to invest in other derivative instruments to the extent it is consistent with the Fund’s investment objectives and restrictions. See “Investment Objective and Principal Investment Strategies — Principal Investment Strategies.”

Convertible Securities.    Investment in convertible securities forms an important part of the Fund’s investment strategies. Under normal circumstances, the Fund will invest at least 20% of its managed assets in convertible securities. A convertible security is a debt security or preferred stock that is exchangeable for an equity security (typically of the same issuer) at a predetermined price (the “conversion price”). Depending upon the relationship of the conversion price to the market value of the underlying security, a convertible security may trade more like an equity security than a debt instrument. The Fund may invest in convertible securities of any rating. See “Investment Objective and Principal Investment Strategies — Principal Investment Strategies — Convertible Securities.”

Synthetic Convertible Securities.    The Fund may invest in “synthetic” convertible securities. A synthetic convertible security is a financial instrument that is designed to simulate the characteristics of another instrument (i.e., a convertible security) through the combined features of a collection of other securities or assets. Calamos may create a synthetic convertible security by combining separate securities that possess the two principal

characteristics of a true convertible security, i.e., a fixed-income security (“fixed-income component”, which may be a convertible or non-convertible security) and the right to acquire an equity security (“convertible component”). The fixed-income component is achieved by investing in fixed-income securities such as bonds, preferred stocks and money market instruments. The convertible component is achieved by investing in warrants or options to buy common stock at a certain exercise price, or options on a stock index.

The Fund may also invest in synthetic convertible securities created by third parties, typically investment banks. Synthetic convertible securities created by such parties may be designed to simulate the characteristics of traditional convertible securities or may be designed to alter or emphasize a particular feature. Traditional convertible securities typically offer the opportunity for stable cash flows with the ability to participate in capital appreciation of the underlying common stock. Traditional convertible securities are exercisable at the option of the holder. Synthetic convertible securities may alter these characteristics by offering enhanced yields in exchange for reduced capital appreciation or additional risk of loss, or any combination of these features. Synthetic convertible instruments may include structured notes, equity-linked notes, mandatory convertibles and combinations of securities and instruments, such as a debt instrument combined with a forward contract. The Fund’s holdings of synthetic convertible securities are considered convertible securities for purposes of the Fund’s policy to invest at least 20% of its managed assets in convertible securities and 80% of its managed assets in a diversified portfolio of convertible securities and below investment grade (high yield/high risk) non-convertible debt securities. See “Investment Objective and Principal Investment Strategies — Principal Investment Strategies — Synthetic Convertible Securities.”

High Yield Securities.    Investment in high yield securities forms an important part of the Fund’s investment strategies. The Fund will invest in high yield securities for either current income or capital appreciation or both. Under normal circumstances, the Fund will invest at least 20% of its managed assets in high yield non-convertible debt securities. These securities are rated Ba or lower by Moody’s Investors Service, Inc. (“Moody’s”) or BB or lower by Standard & Poor’s Financial Services, LLC, a subsidiary of The McGraw-Hill Companies, Inc. (“Standard or Poor’s”) or are unrated securities of comparable quality as determined by Calamos, the Fund’s investment adviser. The Fund may invest in high yield securities of any rating. The Fund may, but currently does not intend to, invest up to 5% of its managed assets in distressed securities that are in default or the issuers of which are in bankruptcy. Non-convertible debt securities rated below investment grade are commonly referred to as “junk bonds” and are considered speculative with respect to the issuer’s capacity to pay interest and repay principal. They involve greater risk of loss, are subject to greater price volatility and are less liquid, especially during periods of economic uncertainty or change, than higher rated securities. See “Investment Objective and Principal Investment Strategies — Principal Investment Strategies — High Yield Securities.”

Foreign Securities.    Although the Fund primarily invests in securities of U.S. issuers, the Fund may invest up to 25% of its managed assets in securities of foreign issuers in developed and emerging markets, including debt and equity securities of corporate issuers and debt securities of government issuers. The Fund may invest up to 15% of its managed assets in securities of foreign issuers in emerging markets. A foreign issuer is a foreign government or a company organized under the laws of a foreign country. See “Investment Objective and Principal Investment Strategies — Principal Investment Strategies — Foreign Securities.”

Rule 144A Securities.    The Fund may invest without limit in certain securities (“Rule 144A Securities”), such as convertible and debt securities, that are typically purchased in transactions exempt from the registration requirements of the 1933 Act pursuant to Rule 144A under that Act. Rule 144A Securities may only be sold to qualified institutional buyers, such as the Fund. Any resale of these securities must generally be effected through a sale that is registered under the 1933 Act or otherwise exempted or excepted from such registration requirements. Under the supervision and oversight of the Fund’s Board of Trustees, Calamos will determine whether Rule 144A Securities are liquid. Typically, the Fund purchases Rule 144A Securities only if Calamos has determined them to be liquid. If any Rule 144A Security held by the Fund should become illiquid, the value of the security may be reduced and a sale of the security may be more difficult. See “Investment Objective and Principal Investment Strategies — Principal Investment Strategies — Rule 144A Securities.”

Options Writing.    The Fund may seek to generate income from option premiums by writing (selling) options. The Fund may write (sell) call options (i) on a portion of the equity securities (including equity

securities obtainable by the Fund through the exercise of its rights with respect to convertible securities it owns) in the Fund’s portfolio and (ii) on broad-based securities indexes (such as the Standard and Poor’s 500^® Index (“S&P 500”) or the MSCI EAFE^® Index (“MSCI EAFE”), which is an index of international equity stocks) or certain ETFs (exchange traded funds) that trade like common stocks but seek to replicate such market indexes.

In addition, to seek to offset some of the risk of a potential decline in value of certain long positions, the Fund may also purchase put options on individual securities, broad-based securities indexes (such as the S&P 500 or MSCI EAFE) or certain ETFs that trade like common stocks but seek to replicate market indexes. See “Investment Objective and Principal Investment Strategies — Options Writing.”

Other Securities.    The Fund may invest in other securities of various types to the extent consistent with its investment objective. Normally, the Fund invests substantially all of its assets to meet its investment objective. For temporary defensive purposes, the Fund may depart from its principal investment strategies and invest part or all of its assets in securities with remaining maturities of less than one year or cash equivalents; or it may hold cash. During such periods, the Fund may not be able to achieve its investment objective. There are no restrictions as to the ratings of debt securities acquired by the Fund or the portion of the Fund’s assets that may be invested in debt securities in a particular ratings category. For more information on the types of derivatives that the Fund invests in, see “Investment Objective and Principal Investment Strategies — Principal Investment Strategies” in this prospectus and “Investment Objective and Policies” in the statement of additional information.

Use of Leverage by the Fund

The Fund currently uses, and may in the future use, financial leverage. The Fund, with the approval of its Board of Trustees, including its independent Trustees, has entered into a financing package that includes a Committed Facility Agreement (the “BNP Agreement”) with BNP Paribas Prime Brokerage International Ltd. (“BNP”) that allows the Fund to borrow up to $240 million, and a securities lending agreement (“Lending Agreement”). In addition, the financing package also includes a Credit Agreement (the “SSB Agreement”) with State Street Bank and Trust Company (“SSB”) that allows the Fund to borrow up to $240 million, and a related securities lending authorization agreement (“Authorized Agreement”) that is used to offset some of the interest rate payments that would otherwise be due in respect of the borrowings under the SSB Agreement. As of January 31, 2016, the Fund had $181 million in borrowings outstanding under the BNP Agreement, representing 15.9% of managed assets as of that date. As of January 31, 2016, the Fund had $181 million in borrowings outstanding under the SSB Agreement, representing 15.9% of managed assets as of that date. Combined borrowings under both agreements as of January 31, 2016 represented $362 million, or 31.8% of managed assets. The Fund will pay, and common shareholders will effectively bear, any costs and expenses relating to any borrowings by the Fund, including the financial leverage described above, as well as any additional financial leverage secured as a result of this offering. Such costs and expenses include the higher management fee resulting from the use of any such leverage, offering and/or issuance costs, and interest and/or dividend expense and ongoing maintenance. See “Leverage” and “Risk Factors — Leverage.”

The Fund may make further use of financial leverage through the issuance of preferred shares or may borrow money or issue additional debt securities to the extent permitted under the 1940 Act. As a non-fundamental policy, the Fund may not issue debt securities, borrow money or issue preferred shares in an aggregate amount exceeding 38% of the Fund’s managed assets measured at the time of issuance of the new securities. However, the Board of Trustees reserves the right to issue preferred shares or debt securities or borrow to the extent permitted by the 1940 Act. See “Leverage.” The holders of preferred shares or debt, if any, on the one hand, and the holders of the common shares, on the other, may have interests that conflict with each other in certain situations. See “Description of Securities — Preferred Shares” and “Certain Provisions of the Agreement and Declaration of Trust and By-Laws, Including Antitakeover Provisions.”

Because Calamos’ investment management fee is a percentage of the Fund’s managed assets, Calamos’ fee will be higher if the Fund is leveraged and Calamos will have an incentive to be more aggressive and leverage the Fund. Consequently, the Fund and Calamos may have differing interests in determining whether to leverage the Fund’s assets. Any additional use of leverage by the Fund effected through new, additional or increased credit

facilities or the issuance of preferred shares would require approval by the Board of Trustees of the Fund. In considering whether to approve the use of additional leverage through those means, the Board would be presented with all relevant information necessary to make a determination whether or not additional leverage would be in the best interests of the Fund, including information regarding any potential conflicts of interest. For further information about the Fund’s financial leverage, see “Use of Leverage by the Fund.”

For further information about the effects of the Fund’s financial leverage and an illustration of the hypothetical effect on the return to a holder of the Fund’s common shares of the leverage obtained by borrowing under the Fund’s financing package, see “Effects of Leverage.” For further information about leveraging, see “Risk Factors — Additional Risks to Common Shareholders — Leverage Risk.”

Interest Rate Transactions

In order to seek to reduce the interest rate risk inherent in the Fund’s underlying investments and capital structure, the Fund, if Calamos deems market conditions favorable, may enter into over-the-counter interest rate swap or cap transactions to attempt to protect itself from increasing dividend or interest expenses on its leverage. The use of interest rate swaps and caps is a highly specialized activity that involves investment techniques and risks different from those associated with ordinary portfolio security transactions.

In an interest rate swap, the Fund would agree to pay to the other party to the interest rate swap (which is known as the “counterparty”) a fixed rate payment in exchange for the counterparty agreeing to pay to the Fund a payment at a variable rate that is expected to approximate the rate on any variable rate payment obligation on the Fund’s leverage. The payment obligations would be based on the notional amount of the swap.

In an interest rate cap, the Fund would pay a premium to the counterparty to the interest rate cap and, to the extent that a specified variable rate index exceeds a predetermined fixed rate, would receive from the counterparty payments of the difference based on the notional amount of such cap. There can be no assurance that the Fund will use interest rate transactions or that, if used, their use will be beneficial to the Fund. Depending on the state of interest rates in general, the Fund’s use of interest rate swap or cap transactions could enhance or harm the overall performance of the common shares. See “Interest Rate Transactions.”

Conflicts of Interest

Conflicts of interest may arise from the fact that Calamos and its affiliates carry on substantial investment activities for other clients, in which the Fund does not have an interest. Calamos or its affiliates may have financial incentives to favor certain of these accounts over the Fund. Any of their proprietary accounts or other customer accounts may compete with the Fund for specific trades. Calamos or its affiliates may give advice and recommend securities to, or buy or sell securities for, other accounts and customers, which advice or securities recommended may differ from advice given to, or securities recommended or bought or sold for, the Fund, even though their investment objectives may be the same as, or similar to, the Fund’s objective.

Situations may occur when the Fund could be disadvantaged because of the investment activities conducted by Calamos and its affiliates for their other accounts. Such situations may be based on, among other things, the following: (1) legal or internal restrictions on the combined size of positions that may be taken for the Fund or the other accounts, thereby limiting the size of the Fund’s position; or (2) the difficulty of liquidating an investment for the Fund or the other accounts where the market cannot absorb the sale of the combined position. See “Investment Objective and Principal Investment Strategies — Conflicts of Interest.”

Fund Risks

Convertible Securities Risk.    The value of a convertible security is influenced by both the yield of non-convertible securities of comparable issuers and by the value of the underlying common stock. The value of a convertible security viewed without regard to its conversion feature (i.e., strictly on the basis of its yield) is sometimes referred to as its “investment value.” A convertible security’s investment value tends to decline as prevailing interest rate levels increase. Conversely, a convertible security’s investment value tends to increase as prevailing interest rate levels decline.

However, the convertible’s market value tends to reflect the market price of the common stock of the issuing company when that stock price is greater than the convertible’s “conversion price.” The conversion price is defined as the predetermined price at which the convertible could be exchanged for the associated stock. As the market price of the underlying common stock declines, the price of the convertible security tends to be influenced more by the yield of the convertible security and changes in interest rates. Thus, the convertible security may not decline in price to the same extent as the underlying common stock. In the event of a liquidation of the issuing company, holders of convertible securities would be paid before the company’s common stockholders. See “Risk Factors — Fund Risks — Convertible Securities Risk.”

Synthetic Convertible Instruments Risk.    The value of a synthetic convertible security may respond differently to market fluctuations than a convertible security because a synthetic convertible is composed of two or more separate securities or instruments, each with its own market value. In addition, if the value of the underlying common stock or the level of the index involved in the convertible component falls below the exercise price of the warrant or option, the warrant or option may lose all value. See “Risk Factors — Fund Risks — Synthetic Convertible Instruments Risk.”

High Yield Securities Risk.    Investment in high yield securities involves substantial risk of loss. Below investment grade non-convertible debt securities or comparable unrated securities are commonly referred to as “junk bonds” and are considered predominantly speculative with respect to the issuer’s ability to pay interest and principal and are susceptible to default or decline in market value due to adverse economic and business developments. The market values for high yield securities tend to be very volatile, and these securities are less liquid than investment grade debt securities. For these reasons, your investment in the Fund is subject to the following specific risks:

Adverse changes in economic conditions are more likely to lead to a weakened capacity of a high yield issuer to make principal payments and interest payments than an investment grade issuer. The principal amount of high yield securities outstanding has proliferated in the past decade as an increasing number of issuers have used high yield securities for corporate financing. An economic downturn could severely affect the ability of highly leveraged issuers to service their debt obligations or to repay their obligations upon maturity.

The secondary market for high yield securities may not be as liquid as the secondary market for more highly rated securities, a factor which may have an adverse effect on the Fund’s ability to dispose of a particular security. There are fewer dealers in the market for high yield securities than for investment grade obligations. The prices quoted by different dealers may vary significantly and the spread between the bid and asked price is generally much larger than for higher quality instruments. Under adverse market or economic conditions, the secondary market for high yield securities could contract further, independent of any specific adverse changes in the condition of a particular issuer, and these instruments may become illiquid. As a result, the Fund could find it more difficult to sell these securities or may be able to sell the securities only at prices lower than if such securities were widely traded. Prices realized upon the sale of such lower rated or unrated securities, under these circumstances, may be less than the prices used in calculating the Fund’s net asset value. See “Risk Factors — Fund Risks — High Yield Securities Risk.”

Interest Rate Risk.    In addition to the risks discussed above, debt securities are subject to certain risks, including:

Leverage Risk.    The Fund has issued indebtedness and may issue preferred shares or borrow money or issue debt securities. As of January 31, 2016, the Fund has leverage in the form of borrowings from SSB and BNP. Leverage is the potential for the Fund to participate in gains and losses on an amount that exceeds the Fund’s investment. The borrowing of money or issuance of debt securities and preferred shares represents the leveraging of the Fund’s common shares. As a non-fundamental policy, the Fund may not issue debt securities, borrow money or issue preferred shares in an aggregate amount exceeding 38% of the Fund’s managed assets measured at the time of issuance of the new securities. However, the Board of Trustees reserves the right to issue preferred shares or debt securities or borrow to the extent permitted by the 1940 Act. See “Leverage.”

Leverage creates risks which may adversely affect the return for the holders of common shares, including:

In addition, the rights of lenders and the holders of preferred shares and debt securities issued by the Fund will be senior to the rights of the holders of common shares with respect to the payment of dividends or to the payment of assets upon liquidation. Holders of preferred shares have voting rights in addition to and separate from the voting rights of common shareholders. See “Description of Securities — Preferred Shares” and “Certain Provisions of the Agreement and Declaration of Trust and By-Laws, Including Antitakeover Provisions.” The holders of preferred shares or debt, if any, on the one hand, and the holders of the common shares, on the other, may have interests that conflict in certain situations.

Leverage is a speculative technique that could adversely affect the returns to common shareholders. Leverage can cause the Fund to lose money and can magnify the effect of any losses. To the extent the income or capital appreciation derived from securities purchased with funds received from leverage exceeds the cost of leverage, the Fund’s return will be greater than if leverage had not been used. Conversely, if the income or capital appreciation from the securities purchased with such funds is not sufficient to cover the cost of leverage or if the Fund incurs capital losses, the return of the Fund will be less than if leverage had not been used, and therefore the amount available for distribution to common shareholders as dividends and other distributions will be reduced or potentially eliminated.

The Fund will pay, and common shareholders will effectively bear, any costs and expenses relating to any borrowings and to the issuance and ongoing maintenance of preferred shares or debt securities. Such costs and expenses include the higher management fee resulting from the use of any such leverage, offering and/or

issuance costs, and interest and/or dividend expense and ongoing maintenance. These conditions may, directly or indirectly, result in higher leverage costs to common shareholders.

Certain types of borrowings may result in the Fund being subject to covenants in credit agreements, including those relating to asset coverage, borrowing base and portfolio composition requirements and additional covenants that may affect the Fund’s ability to pay dividends and distributions on common shares in certain instances. The Fund may also be required to pledge its assets to the lenders in connection with certain types of borrowings. The Fund may be subject to certain restrictions on investments imposed by guidelines of rating agencies which may issue ratings for the preferred shares or short-term debt instruments issued by the Fund. These guidelines may impose asset coverage or portfolio composition requirements that are more stringent than those imposed by the 1940 Act. The Board reserves the right to change the amount and type of leverage that the Fund uses, and reserves the right to implement changes to the Fund’s borrowings that it believes are in the best interests of the Fund, even if such changes impose a higher interest rate or other costs or impacts over the intermediate, or short-term time period. There is no guarantee that the Fund will maintain leverage at the current rate, and the Board reserves the right to raise, decrease, or eliminate the Fund’s leverage exposure. See “Prospectus Summary — Use of Leverage by the Fund.”

Default Risk.    Default risk refers to the risk that a company that issues a convertible or debt security will be unable to fulfill its obligations to repay principal and interest. The lower a debt security is rated, the greater its default risk. As a result, the Fund may incur cost and delays in enforcing its rights against the issuer. See “Risk Factors — Fund Risks — Default Risk.”

Liquidity Risk.    Illiquid securities may be difficult to dispose of at a fair price at the times when the Fund believes it is desirable to do so. Investment of the Fund’s assets in illiquid securities may restrict the Fund’s ability to take advantage of market opportunities. The risks associated with illiquid securities may be particularly acute in situations in which the Fund’s operations require cash and could result in the Fund borrowing to meet its short-term needs or incurring losses on the sale of illiquid securities. See “Risk Factors — Fund Risks — Liquidity Risk.”

Foreign Securities Risk.    Investments in non-U.S. issuers may involve unique risks compared to investing in securities of U.S. issuers. These risks are more pronounced to the extent that the Fund invests a significant portion of its non-U.S investments in one region or in the securities of emerging market issuers. These risks may include:

Emerging Markets Risk.    Emerging market countries may have relatively unstable governments and economies based on only a few industries, which may cause greater instability. The value of emerging market securities will likely be particularly sensitive to changes in the economies of such countries. These countries are also more likely to experience higher levels of inflation, deflation or currency devaluations, which could

adversely affect the value of the Fund’s investments and hurt those countries’ economies and securities markets. See “Risk Factors — Fund Risks — Emerging Markets Risk.”

Risks Associated with Options.    There are several risks associated with transactions in options. For example, there are significant differences between the securities markets and options markets that could result in an imperfect correlation among these markets, causing a given transaction not to achieve its objectives. A decision as to whether, when and how to use options involves the exercise of skill and judgment, and even a well-conceived transaction may be unsuccessful to some degree because of market behavior or unexpected events. The Fund’s ability to utilize options successfully will depend on Calamos’ ability to predict pertinent market movements, which cannot be assured.

The Fund may sell options on individual securities and securities indices. Even though the Fund will receive the option premium to help protect it against loss, a call option sold by the Fund exposes the Fund during the term of the option to possible loss of opportunity to realize appreciation in the market price of the underlying security or instrument and may require the Fund to hold a security or instrument that it might otherwise have sold. In addition, a loss on a call option sold may be greater than the premium received. The Fund may purchase and sell put options on individual securities and securities indices. In selling put options, there is a risk that the Fund may be required to buy the underlying security at a price above the market price. See “Risk Factors — Fund Risks — Risks Associated with Options.”

REIT Risk.    Investing in REITs involves certain unique risks in addition to those risks associated with investing in the real estate industry in general. An equity REIT may be affected by changes in the value of the underlying properties owned by the REIT. A mortgage REIT may be affected by changes in interest rates and the ability of the issuers of its portfolio mortgages to repay their obligations. REITs are dependent upon the skills of their managers and are not diversified. REITs are generally dependent upon maintaining cash flows to repay borrowings and to make distributions to shareholders and are subject to the risk of default by lessees or borrowers. REITs whose underlying assets are concentrated in properties used by a particular industry, such as health care, are also subject to risks associated with such industry. REITs (especially mortgage REITs) are also subject to interest rate risks. If the REIT invests in adjustable rate mortgage loans the interest rates on which are reset periodically, yields on a REIT’s investments in such loans will gradually align themselves to reflect changes in market interest rates. This causes the value of such investments to fluctuate less dramatically in response to interest rate fluctuations than would investments in fixed rate obligations. REITs may have limited financial resources, may utilize significant amounts of leverage, may trade less frequently and in a limited volume and may be subject to more abrupt or erratic price movements than larger company securities. Historically, REITs have been more volatile in price than the larger capitalization stocks included in Standard & Poor’s 500 Stock Index. See “Risk Factors — Fund Risks — REIT Risk.”

Management Risk.    Calamos’ judgment about the attractiveness, relative value or potential appreciation of a particular sector, security or investment strategy may prove to be incorrect. See “Risk Factors — Fund Risks — Management Risk.”

Tax Risk.    The Fund may invest in certain securities, such as certain convertible securities, for which the federal income tax treatment may not be clear or may be subject to re-characterization by the Internal Revenue Service. It could be more difficult for the Fund to comply with the federal income tax requirements applicable to regulated investment companies if the tax characterization of the Fund’s investments is not clear or if the tax treatment of the income from such investments were successfully challenged by the Internal Revenue Service. See “Certain Federal Income Tax Matters.”

Antitakeover Provisions.    The Fund’s Agreement and Declaration of Trust and By-laws include provisions that could limit the ability of other entities or persons to acquire control of the Fund or to change the composition of its Board of Trustees. Such provisions could limit the ability of shareholders to sell their shares at a premium over prevailing market prices by discouraging a third party from seeking to obtain control of the Fund. These provisions include staggered terms of office for the Trustees, advance notice requirements for shareholder proposals, and super-majority voting requirements for certain transactions with affiliates, converting the Fund to an open-end investment company or a merger, asset sale or similar transaction. Holders of preferred shares, if any, may have voting rights in addition to and separate from the voting rights of common shareholders with

respect to certain of these matters. Holders of any preferred shares, voting separately as a single class, have the right to elect at least two Trustees at all times. See “Description of Securities — Preferred Shares” and “Certain Provisions of the Agreement and Declaration of Trust and By-Laws, Including Antitakeover Provisions.” The holders of preferred shares or debt, if any, on the one hand, and the holders of the common shares, on the other, may have interests that conflict, including conflicts that relate to the fees and expenses of the Fund. For more information on potential conflicts of interest between holders of common shares and holders of preferred shares, see “Additional Risks to Common Shareholders — Leverage Risk.” See “Risk Factors — Fund Risks — Antitakeover Provisions.”

Market Disruption Risk.    Certain events have a disruptive effect on the securities markets, such as terrorist attacks, war and other geopolitical events, earthquakes, storms and other disasters. The Fund cannot predict the effects of similar events in the future on the U.S. economy or any foreign economy. See “Risk Factors — Fund Risks — Market Disruption Risk.”

Counterparty and Settlement Risk.    Trading options, futures contracts, swaps and other derivative financial instruments entails credit risk with respect to the counterparties. Such instruments when traded over the counter do not include the same protections as may apply to trading derivatives on organized exchanges. Substantial losses may arise from the insolvency, bankruptcy or default of a counterparty and risk of settlement default of parties with whom it trades securities. This risk may be heightened during volatile market conditions. Settlement mechanisms in emerging markets are generally less developed and reliable than those in more developed countries thus increasing the risks. In the past, broker-dealers and other financial institutions have experienced extreme financial difficulty, sometimes resulting in bankruptcy of the institution. Although Calamos monitors the creditworthiness of the Fund’s counterparties, there can be no assurance that the Fund’s counterparties will not experience similar difficulties, possibly resulting in losses to the Fund. If a counterparty becomes bankrupt, or otherwise fails to perform its obligations under a derivative contract due to financial difficulties, the Fund may experience significant delays in obtaining any recovery under the derivative contract in a bankruptcy or other reorganization proceeding. The Fund may obtain only a limited recovery or may obtain no recovery in such circumstances. Material exposure to a single or small group of counterparties increases the Fund’s counterparty risk. See “Risk Factors — Fund Risks — Counterparty and Settlement Risk.”

Duration Risk.    Duration measures the expected life of a fixed-income security, and its sensitivity to changes in interest rates. The longer a fixed income security’s duration, the more sensitive that security will be to changes in interest rates. Similarly, the longer the Fund’s dollar-weighted average duration, the more sensitive its value will be to interest rate changes than a fund with a shorter dollar-weighted average duration. See “Risk Factors — Fund Risks — Duration Risk.”

Maturity Risk.    Interest rate risk will generally affect the price of a fixed income security more if the security has a longer maturity. Fixed income securities with longer maturities will therefore be more volatile than other fixed income securities with shorter maturities. Conversely, fixed income securities with shorter maturities will be less volatile but generally provide lower potential returns than fixed income securities with longer maturities. The average maturity of the Fund’s investments will affect the volatility of the Fund’s share price. See “Risk Factors — Fund Risks — Maturity Risk.”

Recent Market Events.    Over the last several years, domestic and international markets have experienced acute turmoil. This turmoil resulted in unusual and extreme volatility in the equity and debt markets, in the prices of individual securities and in the world economy. In addition, many governments and quasi-governmental entities throughout the world responded to the turmoil with a variety of significant fiscal and monetary policy changes, including but not limited to, direct capital infusions into companies, new monetary programs and dramatically lower interest rates. An unexpected or quick reversal of these policies could increase volatility in the equity and debt markets. These market conditions and continuing economic risks add significantly to the risk of short-term volatility in the Fund.

Turbulence in the financial markets and reduced liquidity in equity, credit and fixed-income markets may negatively affect issuers worldwide, which could have an adverse effect on the Fund. Following the financial crisis that began in 2007, the Federal Reserve has attempted to stabilize the U.S. economy and support the U.S.

economic recovery by keeping the federal funds rate at or near zero percent. The Federal Reserve recently has sought to raise interest rates, if the Federal Reserve continues to do so, there is a risk that interest rates across the U.S. financial system will rise. These policy changes may expose markets to heightened volatility and may reduce liquidity for certain Fund investments, causing the value of the Fund’s investments and share price to decline.

The response of the international community — through economic sanctions and otherwise — to geopolitical and other events around the globe may have long-term effects on the U.S. and worldwide financial markets and may cause further economic uncertainties in the United States and worldwide. It is difficult to predict how long the securities markets may be affected by these events and/or the effects of these events in the future on the U.S. economy and securities markets. See “Risk Factors — Fund Risks — Recent Market Events.”

The SEC recently issued a proposed rule under the 1940 Act providing for modifications to the regulation of registered investment companies’ use of derivatives and certain related instruments. If adopted, the proposed rule could, among other things, restrict the Fund’s ability to engage in derivatives transactions and related instruments and/or increase the costs of derivatives transactions, such that the Fund may be unable to implement its investment strategies as presently formulated. There can be no assurance that the rule, if adopted, will not adversely affect the Fund and its performance.

Additional Risks to Common Shareholders

Additional risks of investing in common shares include the following:

Interest Rate Transactions Risk.    The Fund may enter into an interest rate swap or cap transaction to attempt to protect itself from increasing dividend or interest expenses on its leverage resulting from increasing short-term interest rates and to hedge its portfolio securities. A decline in interest rates may result in a decline in the value of the swap or cap, which may result in a decline in the net asset value of the Fund. See “Risk Factors — Interest Rate Transactions Risk.”

Reduction of Leverage Risk.    We have previously taken, and may in the future take, action to reduce the amount of leverage employed by the Fund. Reduction of the leverage employed by the Fund, including by redemption of preferred shares, will in turn reduce the amount of assets available for investment in portfolio securities. This reduction in leverage may negatively impact our financial performance, including our ability to sustain current levels of distributions on common shares.

Market Impact Risk.    The sale of our common shares (or the perception that such sales may occur) may have an adverse effect on prices in the secondary market for our common shares by increasing the number of shares available, which may put downward pressure on the market price for our common shares. These sales also might make it more difficult for us to sell additional equity securities in the future at a time and price we deem appropriate.

Diminished Voting Power and Excess Cash Risk.    The voting power of current shareholders will be diluted to the extent that such shareholders do not purchase shares in any future common share offerings or do not purchase sufficient shares to maintain their percentage interest. In addition, if we are unable to invest the proceeds of such offering as intended, our per share distribution may decrease (or may consist of return of capital) and we may not participate in market advances to the same extent as if such proceeds were fully invested as planned.

Market Discount Risk.    The Fund’s common shares have traded both at a premium and at a discount relative to net asset value. Common shares of closed-end investment companies frequently trade at prices lower than their net asset value. Depending on the premium of the Fund’s common shares, the Fund’s net asset value may be reduced immediately following an offering of the Fund’s common shares by the offering expenses paid by the Fund. See “Use of Proceeds.”

In addition to net asset value, the market price of the Fund’s common shares may be affected by such factors as the Fund’s use of leverage, dividend stability, portfolio credit quality, liquidity, market supply and demand of

the common shares and the Fund’s dividends paid (which are, in turn, affected by expenses), call protection for portfolio securities and interest rate movements. See “Leverage,” “Risk Factors” and “Description of Securities.” The Fund’s common shares are designed primarily for long-term investors, and you should not purchase common shares if you intend to sell them shortly after purchase.

See “Risk Factors — Additional Risks to Common Shareholders” for a more detailed discussion of these risks.

Additional Risks to Senior Security Holders

Additional risks of investing in senior securities include the following:

Generally, an investment in preferred shares (including exchange-listed preferred shares) or debt securities (collectively, “senior securities”) is subject to the following risks:

Interest Rate Risk.    Rising market interest rates could impact negatively the value of our investment portfolio, reducing the amount of assets serving as asset coverage for the senior securities. Rising market interest rates could also reduce the value of preferred shares.

Senior Leverage Risk.    Preferred shares will be junior in liquidation and with respect to distribution rights to debt securities and any other borrowings. Senior securities representing indebtedness may constitute a substantial lien and burden on preferred shares by reason of their prior claim against our income and against our net assets in liquidation. We may not be permitted to declare dividends or other distributions with respect to any series of preferred shares unless at such time we meet applicable asset coverage requirements and the payment of principal or interest is not in default with respect to any borrowings.

Ratings and Asset Coverage Risk.    To the extent that senior securities are rated, a rating does not eliminate or necessarily mitigate the risks of investing in our senior securities, and a rating may not fully or accurately reflect all of the credit and market risks associated with that senior security. A rating agency could downgrade the rating of our shares of preferred stock or debt securities, which may make such securities less liquid in the secondary market, though potentially with higher resulting interest rates. If a rating agency downgrades the rating assigned to a senior security, we may alter our portfolio or redeem the senior security. We may voluntarily redeem senior securities under certain circumstances.

Inflation Risk.    Inflation is the reduction in the purchasing power of money resulting from an increase in the price of goods and services. Inflation risk is the risk that the inflation adjusted or “real” value of an investment in preferred stock or debt securities or the income from that investment will be worth less in the future. As inflation occurs, the real value of the preferred shares or debt securities and the dividend payable to holders of preferred stock or interest payable to holders of debt securities declines.

Decline in Net Asset Value Risk.    A material decline in our NAV may impair our ability to maintain required levels of asset coverage for any preferred securities or debt securities we may issue in the future.

Secondary Market Risk.    The market value of exchange-listed preferred shares that the Fund may issue will be determined by factors such as the relative demand for and supply of the preferred shares in the market, general market conditions and other factors beyond the control of the Fund. Because the Fund has no prior trading history for preferred shares, it is difficult to predict the trading patterns of preferred shares, including the effective costs of trading. There is a risk that the market for preferred shares may be thinly traded and relatively illiquid compared to the market for other types of securities.

Market Discount Risk.    The market price of exchange-listed preferred shares that the Fund may issue may also be affected by such factors as the Fund’s use of leverage, dividend stability, portfolio credit quality, liquidity, and the Fund’s dividends paid (which are, in turn, affected by expenses), call protection for portfolio securities and interest rate movements.

Early Redemption Risk.    The Fund may voluntarily redeem preferred shares or may be forced to redeem preferred shares to meet regulatory requirements and the asset coverage requirements of the preferred shares. Such redemptions may be at a time that is unfavorable to holders of the preferred shares.

See “Risk Factors — Additional Risks to Senior Security Holders” for a more detailed discussion of these risks.

SUMMARY OF FUND EXPENSES

The following table and example contain information about the costs and expenses that common shareholders will bear directly or indirectly. In accordance with Commission requirements, the table below shows our expenses, including interest payments on borrowed funds, as a percentage of our average net assets as of October 31, 2015, and not as a percentage of gross assets or managed assets. By showing expenses as a percentage of average net assets, expenses are not expressed as a percentage of all of the assets we invest. The table and example are based on our capital structure as of October 31, 2015.

As of October 31, 2015, the Fund had $366 million in borrowings outstanding and additional structural leverage of $32 million, representing 30.7% of managed assets.

Example:

The following example illustrates the expenses that common shareholders would pay on a $1,000 investment in common shares, assuming (1) total annual expenses of 1.57% of net assets attributable to common shareholders; (2) a 5% annual return; and (3) all distributions are reinvested at net asset value:

The example should not be considered a representation of future expenses. Actual expenses may be greater or less than those assumed. Moreover, our actual rate of return may be greater or less than the hypothetical 5% return shown in the example.