TDF Glide-Path Essentials: Evaluating Fixed Income Exposure

At Vanguard, we are always working to make our target-date funds (TDFs) better. That means regularly reviewing our glide-path design and diving into specific asset allocation topics to ensure that our strategies evolve with the market and continue to meet our clients' needs.

We remain committed to pursuing changes that are guided by purposeful evolution rather than those that are merely cosmetic tweaks. Purposeful evolution requires more than just annual glide-path reviews. It is a continuous process of evaluating how our TDFs can better serve participants and help give them the best chance for a lasting retirement income. Given their widespread use as a qualified default investment alternative (QDIA), changes to TDFs must be carefully considered and justified as meaningful improvements for investor outcomes.

TDF glide path

As part of our ongoing research into TDF asset allocation, we initially selected three topics for deeper analysis: (1) raising the initial equity allocation, (2) assessing inflation-hedging asset classes, and (3) evaluating our fixed income exposure across the glide path. Our preliminary findings indicated that adjusting fixed income exposure could have promising investment potential, which we address here.

Among the fixed income options studied, increasing exposure to long-term U.S. Treasuries across the glide path showed the highest investment value before accounting for implementation factors. However, after further examining performance across various market environments and regimes, operational complexity, cost, and stakeholder feedback, we concluded that the modest investment benefit did not justify the change. Therefore, no adjustments will be made to the Target Retirement Funds glide path at this time.

This article highlights the qualitative, quantitative, and practical considerations surrounding the proposed adjustment to the fixed income allocation and our decision to maintain our existing allocation based on the rigorous standards we set for our Target Retirement series.

How we determine investment merit

In addition to annually reaffirming the appropriateness of the Target Retirement Funds glide path, Vanguard maintains a robust, ongoing TDF research agenda that spans three key areas: glide path and asset allocation, implementation, and the broader TDF ecosystem, including retirement income solutions, advice, and custom offerings.

Every research item is first evaluated for long-term investment merit using our proprietary Vanguard Life-Cycle Investing Model (VLCM), which optimizes glide paths based on utility and key parameters, such as saving rate, expected salary at age 65, and replacement ratio. Using the VLCM allows us to assess the long-term value of glide-path changes through a cost-benefit lens while also evaluating risk-return trade-offs across asset and sub-asset classes.

any meaningful change

The Strategic Asset Allocation Committee (SAAC) governs the glide-path and asset allocation methodology for the Target Retirement Funds and ultimately needs to approve any change made to investment guidelines. Following the initial research into fixed income disaggregation in 2024, the SAAC approved the investment case after review of the CFE and probability of success outcomes from the VLCM assessment. Any research idea that demonstrates sufficient investment merit then undergoes further evaluation through the lens of client needs, business impact, and implementation feasibility. This process ensures that proposed changes move beyond theory to practical application, an especially critical standard for TDFs, which often serve as the plan’s QDIA.

Why not disaggregate fixed income?

A defining strength of the Target Retirement series is its reliability. Its diversified investment approach is designed to support long-term goals and help investors navigate changing market conditions with confidence. This attribute influenced our decision to maintain the current glide path, which was driven by the following factors:

altered portfolio characteristics

potential for performance surprises

investment value eroded