Treasury bill calculator
- 26-week price97.87per $100 (97.866556), Oct 19, 2026
- Investment rate4.372%Treasury auction result
- Formula checks7/7match real auctions
Convert a T-bill price per $100 into its discount rate and investment rate (bond-equivalent yield) with Treasury's published formulas, then see the after-tax rate with or without a state-tax comparison.
Auction data retrieved 2026-10-24 10:58 CDT. Formulas checked Oct 24, 2026.
Calculator
Prefilled from the latest 26-week bill: auction Oct 19, 2026, CUSIP 912797WV5, 182 days, issue Oct 22, 2026.
The calculator needs JavaScript; the formulas are written out below.
Treasury's formulas
- Price per $100 from the discount rate d and days to maturity r: P = 100 × (1 − d × r / 360), rounded to six decimals (TreasuryDirect, Understanding pricing; 31 CFR Part 356, Appendix B).
- Discount rate from a price: d = ((100 − P) / 100) × (360 / r).
- Investment rate, bills of not more than one half-year: i = ((100 − P) / P) × (y / r), where y is 365 or 366 days in the year after issue.
- Investment rate, bills of more than one half-year: solve i² × (r / 2y − 0.25) + i × (r / y) + (P − 100) / P = 0, i = (−b + √(b² − 4ac)) / 2a.
The worked examples are in Treasury's price, yield and rate calculations for a Treasury bill (PDF).
Checked against real auctions
| Bill | Auction | Days | High discount rate | Treasury price | Formula price | Treasury inv. rate | Formula inv. rate | Check |
|---|---|---|---|---|---|---|---|---|
| 4-Week CUSIP 912797VY0 | Oct 22, 2026 | 28 | 3.945% | 99.693167 | 99.693167 | 4.012% | 4.012% | Match |
| 8-Week CUSIP 912797WG8 | Oct 22, 2026 | 56 | 4.015% | 99.375444 | 99.375444 | 4.096% | 4.096% | Match |
| 17-Week CUSIP 912797XA0 | Oct 21, 2026 | 119 | 4.155% | 98.626542 | 98.626542 | 4.271% | 4.271% | Match |
| 6-Week CUSIP 912797VA2 | Oct 20, 2026 | 42 | 3.975% | 99.536250 | 99.536250 | 4.049% | 4.049% | Match |
| 13-Week CUSIP 912797TM9 | Oct 19, 2026 | 91 | 4.095% | 98.964875 | 98.964875 | 4.195% | 4.195% | Match |
| 26-Week CUSIP 912797WV5 | Oct 19, 2026 | 182 | 4.220% | 97.866556 | 97.866556 | 4.372% | 4.372% | Match |
| 52-Week CUSIP 912797WJ2 | Sep 29, 2026 | 364 | 4.400% | 95.551111 | 95.551111 | 4.616% | 4.616% | Match |
Prices are per $100 face; inv. rate = investment rate. Source: TreasuryDirect auction results (securities auctioned feed), retrieved 2026-10-24 10:58 CDT. Formula columns are computed on this page from the high discount rate, days to maturity and days in the year.
After tax
TreasuryDirect lists federal tax due on T-bill interest and no state or local taxes (TreasuryDirect, Treasury bills). The calculator shows the investment rate after the federal rate you enter. With the state toggle on, it also shows the fully taxable rate that would leave the same amount after federal and state tax (after-tax rate ÷ (1 − federal − state)), a flat-rate illustration that ignores deductions and brackets.
To compare T-bills with CDs and savings side by side, see the T-bill vs CD vs savings after-tax yield calculator.
Related: T-bill at TreasuryDirect, step by step · TreasuryDirect vs a brokerage · latest Treasury auction results · Treasury yield curve.
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Frequently asked questions
What is the difference between the discount rate and the investment rate?
Treasury says the discount rate is based on the bill's face value and a 360-day year, while the investment rate (coupon-equivalent yield) is based on the purchase price and a 365-day year (366 in a leap year). Treasury says the investment rate is the one to use when comparing bills with other instruments.
Which formula applies to a 52-week bill?
For bills of more than one half-year to maturity, Treasury solves a quadratic equation for the investment rate. The calculator switches automatically when days to maturity exceed half the days in the year.
Is T-bill interest taxed by states?
TreasuryDirect lists federal tax due on interest earned and no state or local taxes for Treasury bills.
Why might my result differ by a thousandth?
Treasury rounds the price to six decimals and rates to three decimals; it notes that in the case of rounding differences, its determinations are final.
Is this investment advice?
No. The page applies Treasury's published formulas to numbers you enter.