T-Bill Calculator — Price, Yield & Latest Auction Rates

Treasury bills are quoted in a way that trips up newcomers, so this tool translates a discount rate into the figures that actually matter: what you pay up front, the interest you collect, the yield Treasury publishes, and the rate a CD or savings account would need to match it after state tax. Pick a term and it loads the rate and exact length of the most recent auction for that term; a table below lists what a $10,000 bill costs at the latest auction of each term, from 4 to 52 weeks.

The math is Treasury's own (31 CFR 356, Appendix B). The price per $100 is 100 × (1 − discount rate × days / 360), rounded to six decimals, and you pay face value ÷ 100 × that price. The investment rate is (100 − price) ÷ price × 365 ÷ days for bills of half a year or less; for 52-week bills Treasury solves a quadratic that allows for a coupon halfway through, and uses a 366-day year when the year after the issue date contains February 29. Checked against every bill auction from mid-August to late September 2026, the results match Treasury's published prices and investment rates to the last digit.

T-bill interest is federally taxable but exempt from state and local income tax (31 U.S.C. 3124), so a CD or savings account has to pay more to leave you the same after tax. If you itemize, the equivalent yield is the bill's yield ÷ (1 − your state rate); if you take the standard deduction, which most filers do, it is yield × (1 − federal rate) ÷ (1 − federal rate − state rate), a little higher. At the September 21, 2026 auction's 4.303% and a 5% state tax, a CD would need about 4.60% for a standard-deduction filer in the 22% bracket. Rates change at every weekly auction, so check the date on the table.