T-bill calculator: price, interest and investment rate
Enter the discount rate of any Treasury bill, from an auction or a broker quote, and the term. The calculator gives the price, the interest in dollars and the yield to compare with a CD.
Investment rate (bond-equivalent yield)
4.185 %
91 days. You pay $9,896.74 for $10,000 at maturity.
| Price per $100 | 98.967403 |
| You pay | $9,896.74 |
| Interest | $103.26 |
| Yield if rolled at the same rate for a year | 4.251 % |
Price = 100 × (1 − discount × days ÷ 360), rounded to six decimals, as in Treasury auction results. A year with a February 29 inside it uses 366 days.
Worked out by Radif Partners · How we calculate · rates read on treasurydirect.gov and fiscaldata.treasury.gov · not personal financial advice
A Treasury bill calculator turns a discount rate into what you pay and what you earn. The Treasury's formula is price per $100 = 100 × (1 − discount rate × days ÷ 360), rounded to six decimals. With the latest 13-week discount rate of 4.085 % over 91 days, the price is 98.967403, so $10,000 of face value costs $9,896.74 and pays $103.26 of interest at maturity. The investment rate, or bond-equivalent yield, divides that interest by the price and uses a 365-day year: 4.185 %. That is the rate to set against a savings account or a CD. For bills longer than half a year, the Treasury uses a formula with semiannual compounding, which the calculator applies too. The calculator reproduces the investment rate published by the Treasury on 652 bill auctions of 2023 and 2024. It does not include state tax, which bills do not pay: the state tax-equivalent page handles that part.
The same discount rate on every term
Bills of different terms quoted at the same discount rate do not yield the same. The table applies a discount rate of 4.000 % to each term on $10,000: the longer the bill, the further the price falls below face value, and the bigger the gap between the discount rate and the investment rate.
| Term | Days | Price per $100 | Interest | Investment rate | Rolled for a year |
|---|---|---|---|---|---|
| 4-week | 28 | 99.688889 | $31.11 | 4.068 % | 4.145 % |
| 6-week | 42 | 99.533333 | $46.67 | 4.075 % | 4.149 % |
| 8-week | 56 | 99.377778 | $62.22 | 4.081 % | 4.152 % |
| 13-week | 91 | 98.988889 | $101.11 | 4.097 % | 4.160 % |
| 17-week | 119 | 98.677778 | $132.22 | 4.110 % | 4.167 % |
| 26-week | 182 | 97.977778 | $202.22 | 4.139 % | 4.182 % |
| 52-week | 364 | 95.955556 | $404.44 | 4.183 % | 4.227 % |
The last column assumes each bill is replaced at maturity by an identical one at the same price for a full year. It shows why a 4-week bill and a 52-week bill with the same quoted rate are not the same deal: the short bill compounds more often if the rate holds, the long one locks the rate.
Thirteen weeks around today's rate
The next auction will not repeat the last one. The table below moves the 13-week discount rate a quarter point at a time around 4.000 %, to show what a change of that size does to the price and to the interest on $10,000.
| Discount rate | Price per $100 | Cost | Interest | Investment rate |
|---|---|---|---|---|
| 3.500 % | 99.115278 | $9,911.53 | $88.47 | 3.580 % |
| 3.750 % | 99.052083 | $9,905.21 | $94.79 | 3.838 % |
| 4.000 % | 98.988889 | $9,898.89 | $101.11 | 4.097 % |
| 4.250 % | 98.925694 | $9,892.57 | $107.43 | 4.356 % |
| 4.500 % | 98.8625 | $9,886.25 | $113.75 | 4.615 % |
A quarter point of discount on a 13-week bill moves the interest on $10,000 by about $6.32. On a 26-week bill the same move is worth twice as much, on a 4-week bill less than a third.
Price from a discount rate
Investment rate (bond-equivalent yield)
4.351 %
| Price per $100 | 97.876667 |
| You pay | $9,787.67 |
| Interest | $212.33 |
| Yield if rolled at the same rate for a year | 4.398 % |
The formulas, step by step
The Treasury publishes its methods on its pricing page (TreasuryDirect, understanding pricing). Step one, the price: 100 × (1 − d × t ÷ 360), where d is the discount rate and t the days to maturity. Step two, the investment rate for a bill of up to half a year: (100 − price) ÷ price × y ÷ t, where y is 365, or 366 when a February 29 falls in the twelve months after the issue date. Step three, for a longer bill, the Treasury solves a quadratic equation that treats the bill as if it paid interest at six months, like a note. For the latest 52-week bill, priced at 95.551111, the simple formula would give 4.669 %; the Treasury's compounding formula gives 4.616 %, the figure published in the auction result.
The price is rounded to six decimals before the cost is computed, and the cost is rounded to the cent. Interest is the face value minus the cost. The calculator follows the same order, which is why its results match the auction results to the cent.
Checked against the Treasury's own results
The formulas are tested against every regular bill auction of 2023 and 2024 from the Fiscal Data auctions dataset (Fiscal Data), 652 auctions in all, from 4-week to 52-week bills, including the leap year of 2024. For each one, the price computed from the published discount rate equals the published price, and the investment rate equals the published investment rate to the third decimal. Those tests run every time the site is built.
Where the discount rate comes from
For a purchase at auction, the discount rate is unknown until the auction closes, so a calculator can only show what a given rate would produce. The latest T-bill rates give a starting point, and the rate history shows how far rates moved over a year. On the secondary market, brokers quote bills by their discount rate or by their yield, and the calculator converts a discount quote into the yield. Broker fees, if any, are not included. A quote given as a yield rather than a discount rate can be checked by trying discount rates in the calculator until the investment rate matches.
After tax
The interest the calculator shows is taxed by the federal government in the year the bill matures and never by states or localities (31 U.S.C. 3124). Comparing a bill with a fully taxable CD therefore needs one more step, which the T-bill versus CD page does for a given income and state, and the state tax page does for all fifty states and the District of Columbia. How bills are bought and held is on the Treasury bills page.