TIMELY INFORMATION INSIDE

Global Total Return Fund (CGO)

Annual REPORT October 31, 2018

	GO PAPERLESS
	SIGN UP FOR E-DELIVERY

Visit www.calamos.com/FundInvestor/GoPaperless
to enroll. You can view shareholder
communications, including fund prospectuses,
annual reports and other shareholder materials
online long before the printed publications
arrive by traditional mail.

TABLE OF CONTENTS

Letter to Shareholders1

The Calamos Closed-End Funds:
An Overview5

Investment Team Discussion6

Schedule of Investments10

Statement of Assets and Liabilities19

Statement of Operations20

Statements of Changes in Net Assets21

Statement of Cash Flows22

Notes to Financial Statements23

Financial Highlights32

Report of Independent Registered
Public Accounting Firm33

Trustee Approval of
Management Agreement34

Tax Information36

Trustees and Officers37

About Closed-End Funds39

Managed Distribution Policy40

Automatic Dividend Reinvestment Plan40

Experience and Foresight

Our Managed Distribution Policy

Closed-end fund investors often seek a steady stream of income. Recognizing this important need, Calamos closed-end funds adhere to a managed distribution policy in which we aim to provide consistent monthly distributions through the disbursement of the following:

•Net investment income

•Net realized short-term capital gains

•Net realized long-term capital gains

•And, if necessary, return of capital

We set distributions at levels that we believe are sustainable for the long term. Our team focuses on delivering an attractive monthly distribution, while maintaining a long-term emphasis on risk management. The level of the Fund’s distribution can be greatly influenced by market conditions, including the interest rate environment, the individual performance of securities held by the funds, our view of retaining leverage, fund tax considerations, and regulatory requirements.

You should not draw any conclusions about the Fund’s investment performance from the amount of its distribution or from the terms of the Fund’s plan. The Fund’s Board of Trustees may amend or terminate the managed distribution policy at any time without prior notice to the Fund’s shareholders.

For more information about any Calamos closed-end funds, we encourage you to contact your financial advisor or Calamos Investments at 800.582.6959 (Monday through Friday from 8:00 a.m. to 6:00 p.m., Central Time). You can also visit us at www.calamos.com.

Note: The Fund adopted a managed distribution policy on January 1, 2018.

John P. calamos, sr.

Founder, Chairman
and Global Chief
Investment Officer

CALAMOS GLOBAL TOTAL RETURN Fund Annual REPORT   1

Dear Fellow Shareholder:

Welcome to your annual report for the 12-month period ended October 31, 2018. In this report, you will find commentary from the Calamos portfolio management team, as well as a listing of portfolio holdings, financial statements and highlights, and detailed information about the performance and positioning of this Calamos Fund.

Calamos Global Total Return Fund (CGO) is an income-oriented total-return fund. This means we are focused not only on delivering a competitive stream of distributions, but also on total return. We utilize dynamic asset allocation to pursue high current income with a less rate-sensitive approach, while also maintaining a focus on capital gains.

Distribution

During the period, the Fund provided a compelling monthly distribution of $0.1000 per share. We believe the Fund’s current annualized distribution rate, which was 10.43%* on a market price basis as of October 31, 2018, was very competitive, given the low interest rates in many segments of the bond market. In our view, the Fund’s distributions illustrate the benefits of a multi-asset class approach and flexible allocation strategy.

We understand that many closed-end fund investors seek steady, predictable distributions instead of distributions that fluctuate. Therefore, this Fund has a managed distribution policy. As part of this policy, we aim to keep distributions consistent from month to month, and at a level that we believe can be sustained over the long term. In setting the Fund’s distribution rate, the investment management team and the Fund’s Board of Trustees consider the interest rate, market and economic environment. We also factor in our assessment of individual securities and asset classes.

*Current Annualized Distribution Rate is the Fund’s most recent distribution, expressed as an annualized percentage of the Fund’s current market price per share. The Fund’s 10/31/18 distribution was $0.1000 per share. Based on our current estimates, we anticipate that approximately $0.0117 is paid from ordinary income or capital gains and that approximately $0.0883 represents a return of capital. Estimates are calculated on a tax basis rather than on a generally accepted accounting principles (GAAP) basis, but should not be used for tax reporting purposes. Distributions are subject to re-characterization for tax purposes after the end of the fiscal year. This information is not legal or tax advice. Consult a professional regarding your specific legal or tax matters. Under the Fund’s managed distribution policy, distributions paid to common shareholders may include net investment income, net realized short-term capital gains and return of capital. When the net investment income and net realized short-term capital gains are not sufficient, a portion of the distribution will be a return of capital. In addition, a limited number of distributions per calendar year may include net realized long-term capital gains. The distribution rate may vary.

2   CALAMOS GLOBAL TOTAL RETURN Fund Annual REPORT

Market Review

The global economy continued to expand during the reporting period, with especially strong fundamentals in the United States. Nonetheless, markets experienced turbulence, with non-U.S. markets facing the greatest pressures. A variety of factors contributed to investor apprehension, including trade policy uncertainty, rising U.S. interest rates, political uncertainties, and fears of softening global growth. In October, anxiety intensified, resulting in a sell-off across global financial markets.

For the 12 months overall, U.S. stocks and convertible securities outperformed global averages.¹ Within the fixed income market, high yield securities and shorter-term bonds were more resilient than investment-grade and longer-term issues.²

Outlook

The U.S. economy is likely to maintain its growth trajectory through 2019. Unemployment is low, inflation is contained, consumer and small business confidence are strong, and capital spending is increasing. Deregulation and tax reform have already provided a powerful tailwind for U.S. economic activity and corporate earnings, but we believe the full measure of these policies has yet to be fully reflected in the economy. We expect the Federal Reserve to continue raising interest rates slowly in response to healthy economic conditions, but we do not believe these gradual increases represent an imminent threat to the U.S. economy or markets. Political gridlock is likely, which market participants may welcome if the fiscal policies put in place over recent years remain intact.

Outside the U.S., economic fundamentals are less strong on a relative basis and there is a wide range of political unknowns. However, there are a number of potential tailwinds for growth, such as more stimulative fiscal policy in China and Europe, and supportive policies from global central banks. Additionally, many global investments are trading at what we believe are attractive prices.

As we look forward, we see continued opportunities in stocks, as well as in other economically sensitive areas of the market, such as convertible securities and high yield bonds. Selectivity and risk management will remain essential: political, geopolitical, and interest rate uncertainties are likely to contribute to ongoing market volatility and shifts in market leadership as the economic cycle matures.

We believe the Fund is well positioned for the environment we expect. Our portfolio management team employs rigorous research to take advantage of the volatility in the markets, adding to positions when valuations are attractive and locking in gains when prices rise. They remain highly attentive to the interests of the shareholders in the Fund, including the need for appropriate levels of downside risk management.

CALAMOS GLOBAL TOTAL RETURN Fund Annual REPORT   3

Conclusion

On behalf of all of us at Calamos Investments, thank you for entrusting us with your assets. I encourage you to visit our website, www.calamos.com, on an ongoing basis for updates about the Fund and the markets, as well as additional information about asset allocation.

Sincerely,

John P. Calamos, Sr.

Founder, Chairman and Global Chief Investment Officer

4   CALAMOS GLOBAL TOTAL RETURN Fund Annual REPORT

CALAMOS GLOBAL TOTAL RETURN Fund Annual REPORT   5

In our closed-end funds, we draw upon decades of investment experience, including a long history of opportunistically blending asset classes in an attempt to capture upside potential while seeking to manage downside risk. We launched our first closed-end fund in 2002.

Closed-end funds are long-term investments. Most focus on providing monthly distributions, but there are important differences among individual closed-end funds. Calamos closed-end funds can be grouped into multiple categories that seek to produce income while offering exposure to various asset classes and sectors.

6   CALAMOS GLOBAL TOTAL RETURN Fund Annual REPORT

TOTAL RETURN* AS OF 10/31/18

SECTOR WEIGHTINGS

Sector Weightings are based on managed assets and may vary over time. Sector Weightings exclude any government/sovereign bonds or options on broad market indexes the Fund may hold.

Global Total Return Fund (CGO)

INVESTMENT TEAM DISCUSSION

Please discuss the Fund’s strategy and role within an asset allocation.

Calamos Global Total Return Fund (CGO) is a global total return oriented offering that seeks to provide an attractive monthly distribution. The Fund invests in a diversified portfolio of global equities, convertible securities and high yield securities. The allocation to each asset class is dynamic and reflects our view of the economic landscape as well as the potential of individual securities. By combining these asset classes, we believe that the Fund’s portfolio is well positioned to generate capital gains and income. This broader range of security types also provides us with increased opportunities to manage the risk/reward characteristics of the portfolio over full market cycles. Through this approach, the Fund seeks to offer investors an attractive monthly distribution and equity participation.

We believe having a relatively high level of exposure to convertible and equity assets is optimal for the portfolio and reflects our cautiously optimistic view of the global stock markets, albeit on a selective and risk-managed basis. We continue to find new opportunities in the convertible market as issuance of these securities has expanded globally over the course of the year. We believe that maintaining a high exposure to the equity markets via stocks and convertibles was beneficial to the overall performance of the Fund, as these markets offered positive returns for the reporting period.

The Fund invests in both U.S. and non-U.S. companies, favoring companies with geographically diversified revenue streams and global business strategies. We emphasize companies we believe offer reliable debt servicing, respectable balance sheets and sustainable prospects for growth.

How did the Fund perform over the reporting period?

The Fund returned -5.06% on a net asset value (NAV) basis for the 12 months ended October 31, 2018. On a market price basis, the Fund decreased -10.17%. In comparison, the broad global equity market was up 1.71% for the same period, as measured by the MSCI World Index.

At the end of the reporting period, the Fund’s shares traded at a -1.29% discount to net asset value.

How do NAV and market price return differ?

Closed-end funds trade on exchanges, where the price of shares may be driven by factors other than the value of the underlying securities. The price of a share in the market is called market value. Market price may be influenced by factors unrelated to the performance of the fund’s holdings, such as general market sentiment or future expectation. A fund’s NAV return measures the actual return of the individual securities in the portfolio, less fund expenses. It also measures how a manager was able to capitalize on market opportunities. Because we believe closed-end funds are best utilized long term within asset allocations, we believe that NAV return is the better measure of a fund’s performance. However, when managing the fund, we strongly consider actions and policies that we believe will optimize its overall price performance and returns based on market value.

CALAMOS GLOBAL TOTAL RETURN Fund Annual REPORT   7

SINCE INCEPTION MARKET PRICE AND NAV HISTORY THROUGH 10/31/18

Performance data quoted represents past performance, which is no guarantee of future results. Current performance may be lower or higher than the performance quoted. The principal value of an investment will fluctuate so that your shares, when sold, may be worth more or less than their original cost. Returns at NAV reflect the deduction of the Fund’s management fee, debt leverage costs and all other applicable fees and expenses. You can obtain performance data current to the most recent month end by visiting www.calamos.com.

Please discuss the Fund’s distributions during the one-year period.

We employ a managed distribution policy* within this Fund with the goal of providing shareholders a consistent distribution stream. In each month of the period, the Fund distributed $0.1000 per share, resulting in a current annualized distribution rate of 10.43% of market price as of October 31, 2018.

We believe that both the Fund’s distribution rate and level remained attractive and competitive, as low-but-rising interest rates limited yield opportunities in much of the marketplace. For example, as of October 31, 2018, the dividend yield of S&P 500 Index stocks averaged approximately 1.88%.^† Yields also were low within the U.S. government bond market, with the 10-year U.S. Treasury and 30-year U.S. Treasury yielding 3.15% and 3.39%, respectively.^‡

What factors influenced performance over the reporting period?

The portfolio has a wide set of investment parameters that allow us to take advantage of investment opportunities around the world through many different types of investment vehicles. By optimizing the advantages of flexibility, the Fund invested opportunistically. The Fund maintained its exposure to the equity markets, and both convertibles and high yield bonds provided income to the portfolio for the period. The strength and performance of global equity and fixed income markets buoyed both price and NAV performance for the period.

Our selection in financials, notably in diversified banks, was additive to performance relative to the MSCI World Index. In addition, our selection in utilities (multi-utilities) was helpful to performance.

*Under the Fund’s managed distribution policy, distributions paid to common shareholders may include net investment income, net realized short-term capital gains and return of capital. When the net investment income and net realized short-term capital gains are not sufficient, a portion of the distribution will be a return of capital. In addition, a limited number of distributions per calendar year may include net realized long-term capital gains. The distribution rate may vary.

†Source: Standard & Poor’s

‡Source: U.S. Department of the Treasury

8   CALAMOS GLOBAL TOTAL RETURN Fund Annual REPORT

Conversely, our selection in information technology, notably the Fund’s holdings in wireless telecommunication services, proved detrimental relative to the index. In addition, selection in consumer discretionary, namely internet and direct marketing retail, impeded results.

How is the Fund positioned?

The Fund’s heaviest allocations are within the financials, information technology and consumer discretionary sectors. We are relatively optimistic regarding the global economy, with an emphasis on the U.S. and companies that benefit from the wallet of the U.S. consumer. We favor quality growth companies with higher-quality balance sheets, strong brands, free cash flows and experienced management. We seek to invest in businesses poised to benefit from increased capital spending in technologies, the global infrastructure build-out, and U.S. consumer optimism, demographics and spending power. We favor financials as we expect rising interest rates, a reflationary economic environment and less onerous regulations will benefit the sector.

We favor companies with compelling growth opportunities and global revenue drivers. Improving global business dynamics are providing opportunities in the information technology field. For example, businesses and individuals continue to focus on productivity enhancements, stimulating demand for technology and services. In response, we maintain a heavy overweight position in this area relative to the MSCI World Index. Conversely, our weight to utilities is notably below the index weighting, as we do not see utilities as an area that will realize attractive growth given our outlook.

The average credit quality of rated securities within the portfolio is approximately BB, which is higher than the Credit Suisse U.S. High Yield index. This is typical for the Fund, as our credit process tends to guide us away from the most speculative corporate securities. That said, we do selectively invest in lower-credit securities when we believe the risk/reward dynamics are favorable for our investors.

We believe that this is an environment that is conducive to the prudent use of leverage as a means of enhancing total return and supporting the fund’s distribution rate. In spite of a cost increase due to rising interest rates, the Fund’s use of leverage over the period enjoyed a favorable reinvestment dynamic. As of October 31, 2018, the Fund’s amount of leveraged assets was approximately 35%.

What are your closing thoughts for Fund shareholders?

Given our outlook for a continued period of economic growth, we are favoring quality growth companies over cyclicals. Favorable factors within the U.S. include solid job creation, still low interest rates and range-bound energy prices, increasing consumer and corporate confidence and limited inflationary pressures. We are emphasizing investments in companies with solid cash flow generation and stronger balance sheets. From a thematic and sector perspective, we see opportunities in the technology sector, consumer discretionary companies tied to U.S. and global consumption, and companies positioned to benefit from improving fundamentals. We are also optimistic about financials, as we believe that many of these companies are favorably valued and positioned to grow revenues in a lower regulatory, rising interest rate environment. We believe U.S. consumer discretionary companies offer favorable dynamics given the healthy optimism and market of the U.S. consumer. However, we are also cautious about companies in the consumer staples sector. We believe they may be fully valued as

CALAMOS GLOBAL TOTAL RETURN Fund Annual REPORT   9

investors are attracted to those stocks for income rather than growth. We are selective regarding the health care sector, favoring those companies that are more product growth oriented versus price driven. We believe our active, risk-managed investment approach positions the Fund to take advantage of the volatility and opportunities in global equities and convertible securities.

This information is not intended to be a recommendation or investment advice, and does not constitute a solicitation to buy or sell securities. Certain statements in this commentary are forward-looking statements. Discussions of specific investments are for illustration only and are not intended as recommendations of individual investments. The forward looking statements and other views expressed herein are those of the portfolio managers as of the date of this report. Actual future results or occurrence may differ significantly from those anticipated in any forward-looking statements and the views expressed herein are subject to change at any time, due to numerous market and other factors. The Fund disclaims any obligation to update publicly or review any forward-looking statements or views expressed herein.