Strategy
T-Bill Reinvestment: Roll or Lock In a Year? (Oct 7, 2026)
The bill market is pricing 3-month rates to rise from 4.12% today to about 4.45% by July 2027. If that happens, rolling 13-week bills and locking in today's 52-week bill at 4.34% earn the same over the year.
Locking in earns more if rates come in below that path: if they stay where they are, the 52-week bill earns $23 more on $10,000. Rolling earns more only if rates climb faster than the market prices.
These are calculations derived from publicly available U.S. Treasury data. They are not investment advice or a recommendation to buy or sell any security.
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Roll or lock in, one bill at a time
4 bills over the year, each held until it matures and then rolled into the next. The first is bought today at 4.12%; the market prices the last, bought around Jul 7, at 4.45%.
| Over the next year | Roll 13-week | Lock in 52-week | Earns more |
|---|---|---|---|
| Rates move as the market prices them | 4.39% ($439) | 4.39% ($439) | Same |
| Rates stay at today's level | 4.17% ($417) | 4.39% ($439) | 52-week bill |
| Rates end up 0.5 points higher than priced | 4.78% ($478) | 4.39% ($439) | Rolling |
| Rates end up 0.5 points lower than priced | 4.01% ($401) | 4.39% ($439) | 52-week bill |
Each purchase and the rate priced in
- Today: 4.12%
- Jan 6: 4.38%
- Apr 7: 4.43%
- Jul 7: 4.45%
Return for the year on $10,000, with the interest in brackets, every maturing bill reinvested in full, before taxes. The return is the interest divided by the amount, so it sits slightly above the quoted investment rate, which is stated with semiannual compounding. Treasury bill interest is exempt from state and local income tax. Rates priced in are what today's bill prices imply, not a forecast by Safe Rate.¹
The rate rolling needs to catch up
| Keep rolling | Rate today | Later bills need to average |
|---|---|---|
| 4-week bills | 3.94% | 4.38% |
| 13-week bills | 4.12% | 4.42% |
| 26-week bills | 4.25% | 4.44% |
To match locking in the 52-week bill at 4.34%, the bills bought after today's must average at least this much over the rest of the year.
How reinvestment works
A Treasury bill pays its face value at maturity. Rolling means buying a new bill with the proceeds, at whatever rate that week's auction sets. TreasuryDirect and many brokers can do this automatically, reinvesting a maturing bill into the same term.
Rolling short bills keeps money available sooner and follows rates as they move, up or down. Holding a 52-week bill fixes the rate for the year. Which earns more depends only on where bill rates go, and the catch-up rate above is the line between the two.
Sources
- Rates: Safe Rate's bill curve, a Nelson-Siegel curve fitted each business day to Treasury's end-of-day prices for every bill with at least two weeks to maturity, for Oct 7, 2026. Prices are a U.S. government publication.
- ¹ The rates priced in are implied forward rates, calculated from the bill curve's discount factors on a bond-equivalent basis, the basis TreasuryDirect calls the investment rate. Bill prices also reflect how many bills Treasury is selling and what investors pay for shorter maturities, so they are the market's price for later rates rather than a pure prediction. Futures on SOFR and fed funds price the same question more directly. How the coupon curve is fitted: Treasury curve methodology.