This article was produced by Symetra Investment Management as part of their valued industry partnership with Insurance Investor.
By John Flynn, CFA, Senior Managing Director – Business Development & Marketing, Symetra Investment Management.
The US Aggregate Bond Index is a market capitalisation-weighted benchmark which endeavours to represent most of the investment-grade bond market in the US, including treasuries, agencies, corporate, mortgage-backed, and a smaller component of other securitised bonds. The index got its official start in 1986 and, to the chagrin of more than a few investors, has undergone several name changes over the past few decades. Originally known as the “Lehman Aggregate Bond Index,” the name changed to the “Barclays Capital Aggregate Bond Index” in 2008 after Lehman Brothers succumbed to the Great Financial Crisis. That name was held until 2016, when Bloomberg purchased Barclays’ index business in 2016. Today, the index is formally called the “Bloomberg US Aggregate Bond Index” (“Aggregate”) and, as of May 29, 2026, represented almost 14,000 issues and $31 trillion in market value of US investment-grade bonds. Almost all Core, Core Plus, and Multi-Sector bond market mandates use the index as their primary performance benchmark.
Given the longer liabilities of most fixed income allocators, the duration mismatch of the benchmark has been largely accepted due to its broad exposure, history and transparency. Over the last several decades, the underlying constituents and sectors have undergone a structural but meaningful change that has significantly increased the exposure to the US Treasury market, subsequently increasing the index’s duration and reducing the yield available to investors.
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