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Slower money market fund (MMF) inflows can put Treasury bill yields higher than they otherwise would be if funds consequently make fewer bill purchases. That is a conditional market effect, not a guarantee that yields will rise: the result also depends on Treasury bill supply, expected Federal Reserve policy rates, and whether funds direct cash to bills, repo, or other investments.
Why slower fund flows can put upward pressure on bill yields
When investors add money to MMFs, managers allocate that cash among eligible short-term investments. Treasury bills are an important destination, but not the only one. If inflows slow and funds therefore buy fewer bills than they otherwise would, demand at the margin is weaker. With supply and other conditions unchanged, weaker demand tends to mean lower bill prices and higher yields relative to that counterfactual.
The link depends on where the money goes. Federal Reserve staff describe bills as a significant MMF investment and as close substitutes for repo lending: “Additionally, MMFs invest a significant portion of their portfolios in Treasury bills, which are close substitutes for their lending in repo markets.” (Federal Reserve staff note, August 26, 2026.) A fund may redirect cash from bills to repo, or the other way around, rather than stop investing. Total MMF asset growth therefore is not the same thing as bill purchases.
What can outweigh the flow effect?
Treasury bill supply
Yields respond to the balance between demand and the amount of bills investors must absorb. The Federal Reserve’s July 2024 report linked increased net bill supply to upward pressure on bill yields relative to the ON RRP offering rate. It also noted that the later slowdown in the decline of ON RRP usage was primarily associated with reduced net bill supply, illustrating why changes in fund behavior cannot be read in isolation. (Federal Reserve, July 2024 Financial Stability Report.)
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Expected policy rates
Bill yields reflect expectations about short-term interest rates as well as current buying and selling. If expected policy rates fall, bill yields can decline even while slower MMF inflows exert upward pressure relative to what yields would otherwise have been. The flow channel does not determine the overall direction.
Fund allocation and market conditions
MMFs can hold bills, lend in repo, and invest in other permitted assets. A change in flows may alter demand across these markets differently. Liquidity and repo conditions also matter: a repo-rate movement is not itself a Treasury bill-yield movement, even when the markets are connected.
How the rate cycle can affect MMF flows
Flow patterns can lag changes in interest rates. A U.S. Treasury Borrowing Advisory Committee presentation in Q3 2024 described MMF assets as tracking a rate-cutting cycle with a 12-to-24-month lag. It also said funds can receive inflows immediately before rate cuts because managers may extend weighted average maturity, delaying the decline in fund yields and keeping them attractive versus alternatives such as short-term bank CDs. This is a historical relationship described in that presentation, not a timing rule for every cycle. (U.S. Treasury Borrowing Advisory Committee, Q3 2024 presentation.)
In its Q2 2026 presentation, the committee expected MMF growth to moderate after rapid expansion from 2022 through 2025, citing the spread between money-market and bank deposit rates and an inverted yield curve as contributing factors. It said recent rate easing could potentially slow or reverse those trends, though that had not yet materialized when the presentation was prepared, and characterized MMFs as likely to remain a very large source of T-bill demand. These were dated committee expectations, not a guarantee about subsequent flows. (U.S. Treasury Borrowing Advisory Committee, Q2 2026 presentation.)
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What the available numbers do—and do not—show
A Federal Reserve staff analysis estimated that $100 billion of net Treasury bill issuance was associated with a 1.3-basis-point increase in the daily TGCR-IORB repo-rate spread. The estimate comes from a daily regression covering September 2014 to March 2026. It measures a repo-spread association, not the effect of MMF flows on Treasury bill yields. The note also reports that the negative association between changes in government MMF assets and repo spreads was only marginally significant. Neither result is a bill-yield forecast. (Federal Reserve staff note, August 26, 2026; associated analysis.)
The sources do not provide a directly identified current estimate of how many basis points Treasury bill yields move solely because MMF flows slow. A specific yield prediction would require more than the flow trend: it would need to account for bill issuance, the funds’ actual allocations, and changing expectations for short-term rates.
Quick Recap
A practical way to read a slowdown in MMF flows
- Check where fund cash is going. Slower asset growth matters for bills only to the extent it means weaker bill purchases rather than a shift among bills, repo, or other assets.
- Compare demand with net bill supply. More issuance can add upward pressure on yields; less issuance can ease the amount of supply private investors must absorb.
- Separate relative pressure from the outright move. “Higher than otherwise” describes the flow effect against a counterfactual. Yields can still fall if other forces, such as lower expected policy rates, dominate.
- Keep repo rates distinct from bill yields. The markets are linked, but a measured change in a repo spread cannot be presented as a measured change in Treasury bill yields.
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