Originally designed to represent the investment-grade fixed-income universe, the composition and risk profile of the Agg have lagged the evolution of the fixed-income landscape. The index includes only securities that are U.S. dollar-denominated, investment-grade rated by three agencies (Moody’s, S&P, and Fitch), fixed rate, and taxable. The Agg also has minimum issue size requirements that narrow its constituents to larger, less varied bonds.
These features limit inclusion to more liquid issues at the expense of a broad range of fixed-income securities that can offer investors diversification and excess return potential. Key sectors underrepresented or entirely absent from the Agg include asset-backed securities (ABS), collateralized loan obligations (CLOs), residential mortgage-backed securities (RMBS), commercial mortgage-backed securities (CMBS), high yield bonds, commercial real estate (CRE) loans, leveraged loans, and private debt, as well as any floating-rate or tax-exempt securities. Importantly, the Agg excludes privately placed, unregistered securities entirely, limiting its coverage of a large and rapidly growing segment of the fixed-income market.
The Agg Is Increasingly Concentrated in Treasury Securities
The sharp rise in federal deficits since 2008 has reshaped the composition of the Agg by dramatically increasing the supply of U.S. Treasurys. Marketable U.S. Treasury securities have grown at an average annual rate of 12 percent since 2009, far outpacing the growth of nonfinancial corporate debt (4 percent) and financial institution debt (1 percent). As a result, the U.S. government has become the dominant borrower in public bond markets. This shift has driven Treasurys’ share of the Agg from just 21 percent in 2007 to 44 percent today—concentrating duration and rate sensitivity in benchmark-constrained portfolios.
Important Notices and Disclosures
The Bloomberg U.S. Aggregate Bond Index is a broad-based flagship benchmark that measures the investment grade, US dollar-denominated, fixed-rate taxable bond market.
The index includes Treasurys, government-related and corporate securities, MBS (Agency fixed-rate and hybrid ARM pass-throughs), ABS, and CMBS (Agency and non-Agency).
The Bloomberg U.S. Aggregate ABS Index is component of the Bloomberg U.S. Aggregate Index, the Bloomberg U.S. Aggregate ABS Index includes pass-through, bullet and controlled amortization structures. The Index includes only the senior class of each ABS issue and the ERISA-eligible B and C tranche.
The Bloomberg U.S. CMBS Investment-Grade Index measures the market of U.S. Agency and U.S. non-Agency conduit and fusion CMBS deals with a minimum current deal size
of $300m.
The Bloomberg U.S. Corporate Bond Index measures the investment grade, fixed-rate, taxable corporate bond market. It includes USD denominated securities publicly issued by U.S. and non-U.S. industrial, utility, and financial issuers.
The Bloomberg U.S. MBS Index consists of the MBS assets within the Bloomberg Aggregate Index.
The Bloomberg U.S. Municipal Bond Index is a broad-based benchmark that measures the investment grade, USD-denominated, fixed tax-exempt bond market. The index includes state and local general obligation, revenue, insured, and pre-refunded bonds.
The Bloomberg U.S. Treasury Index measures U.S. dollar-denominated, fixed-rate, nominal debt issued by the U.S. Treasury. Treasury bills are excluded by the maturity constraint, but are part of a separate Short Treasury Index. STRIPS are excluded from the index because their inclusion would result in double-counting.
The Bloomberg U.S. Corporate High-Yield Bond Index measures the USD-denominated, high yield, fixed-rate corporate bond market. Securities are classified as high yield if the middle rating of Moody’s, Fitch and S&P is Ba1/BB+/BB+ or below.
The S&P UBS Leveraged Loan Index is designed to mirror the investable universe of the USD-denominated leveraged loan market.
The ICE BofA U.S. Fixed & Floating Rate Asset Backed Securities Index tracks the performance of USD-denominated investment-grade asset backed securities publicly issued in the US domestic market.
The ICE BofA AA-BBB U.S. Fixed Rate Asset Backed Index is the AA-rated to BBB-rated subset of the ICE BofA U.S. Fixed Rate Asset Backed Securities Index, which tracks the performance of USD-denominated investment-grade fixed rate asset backed securities publicly issued in the U.S. domestic market.
The Palmer Square CLO Senior Debt Index is also a rules-based observable pricing and total return index for CLO debt for sale in the United States, rated at the time of issuance as AAA or AA or equivalent rating. Such debt is often referred to as the senior tranches of a CLO.
The Palmer Square CLO Debt Index is a rules-based observable pricing and total return index for collateralized loan obligation debt for sale in the United States, original rated A, BBB, or BB or equivalent rating.
Past performance does not guarantee future results.
Investing involves risk, including the possible loss of principal. In general, the value of a fixed-income security falls when interest rates rise and rises when interest rates fall. Longer term bonds are more sensitive to interest rate changes and subject to greater volatility than those with shorter maturities. During periods of declining rates, the interest rates on floating rate securities generally reset downward and their value is unlikely to rise to the same extent as comparable fixed rate securities. High yield and unrated debt securities are at a greater risk of default than investment grade bonds and may be less liquid, which may increase volatility. Investors in asset-backed securities, including mortgage-backed securities and collateralized loan obligations (“CLOs”), generally receive payments that are part interest and part return of principal. These payments may vary based on the rate loans are repaid. Some asset-backed securities may have structures that make their reaction to interest rates and other factors difficult to predict, making their prices volatile and they are subject to liquidity and valuation risk. CLOs bear similar risks to investing in loans directly, such as credit, interest rate, counterparty, prepayment, liquidity, and valuation risks. Loans are often below investment grade, may be unrated, and typically offer a fixed or floating interest rate. Private debt investments are generally considered illiquid and not quoted on any exchange; thus they are difficult to value. The process of valuing investments for which reliable market quotations are not available is based on inherent uncertainties and may not be accurate. Further, the level of discretion used by an investment manager to value private debt securities could lead to conflicts of interest. There is no guarantee that an active manager's views will produce the desired results or expected returns, which may lead to underperformance. Actively managed investments generally charge higher fees than passive strategies, which could affect performance. In addition, active and frequent trading that can accompany active management, also called "high turnover," may lead to higher brokerage costs and have a negative impact on performance. Further, active and frequent trading may lead to adverse tax consequences.
This material is distributed or presented for informational or educational purposes only and should not be considered a recommendation of any particular security, strategy or investment product, or as investing advice of any kind. This material is not provided in a fiduciary capacity, may not be relied upon for or in connection with the making of investment decisions, and does not constitute a solicitation of an offer to buy or sell securities. The content contained herein is not intended to be and should not be construed as legal or tax advice and/or a legal opinion. Always consult a financial, tax and/or legal professional regarding your specific situation.
This material contains opinions of the author, but not necessarily those of Guggenheim Partners, LLC or its subsidiaries. The opinions contained herein are subject to change without notice. Forward looking statements, estimates, and certain information contained herein are based upon proprietary and non-proprietary research and other sources. Information contained herein has been obtained from sources believed to be reliable, but are not assured as to accuracy. Past performance is not indicative of future results. There is neither representation nor warranty as to the current accuracy of, nor liability for, decisions based on such information.
© 2025, Guggenheim Partners, LLC. No part of this article may be reproduced in any form, or referred to in any other publication, without express written permission of Guggenheim Partners, LLC. Guggenheim Funds Distributors, LLC is an affiliate of Guggenheim Partners, LLC. For information, call 800.345.7999 or 800.820.0888.
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