T-Bill Calculator

Calculate the price, maturity interest, investment rate, and after-tax return for a 4-week, 8-week, 13-week, 26-week, or 52-week Treasury bill. Built for the exact question: what will this T-bill pay me after federal tax?

Interest at maturity

$37

Buy for $9,963 and receive $10,000 at maturity.

Yield math

Investment rate
4.885%
Purchase price
$9,963
Maturity value
$10,000

Tax estimate

Federal tax
$8
State tax avoided
$2
After-tax interest
$29

Bank APY comparison

A taxable bank account would need about 5.220% APY to match this T-bill after taxes.

How to use this calculator

  1. Enter the face value you plan to buy. Treasury bills mature at this amount.
  2. Choose the term and enter the auction or brokerage discount rate.
  3. Add your federal and state marginal tax rates to estimate the after-tax interest and taxable bank APY needed to match it.

How it works: the math

Treasury bills do not pay monthly interest. They are sold below face value and mature at face value. The calculator uses the standard discount-rate price formula: price = face value x (1 - discount rate x days / 360). The difference between price and face value is the interest you earn if you hold to maturity.

A fully worked example. A $10,000 4-week T-bill at a 4.8% discount rate costs $9,963and matures at $10,000, creating $37 of interest. At a 22% federal bracket, estimated federal tax is $8, leaving $29 after federal tax.

TreasuryDirectsays bills mature in one year or less and are sold at a discount or at par; for bills, interest is the difference between the purchase price and the face value paid at maturity. Treasury interest is taxable federally and exempt from state and local income tax.

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Frequently asked questions

How do I calculate T-bill interest?

Treasury bills are sold at a discount and mature at face value. Interest is the difference between the face value you receive at maturity and the discounted purchase price you paid.

How do I calculate the price of a 4 week T-bill?

Use the quoted discount rate, the number of days to maturity, and the face value. This calculator uses price = face value x (1 - discount rate x days / 360), then shows the interest earned when the bill matures.

What is the difference between T-bill discount rate and investment rate?

The discount rate is quoted against face value on a 360-day year. The investment rate, often called bond-equivalent yield, annualizes the return against the price you actually pay, using a 365-day year. The investment rate is usually the better number to compare with bank APYs.

Are T-bill earnings taxable?

Yes federally. Treasury bill interest is taxable at the federal level, but it is exempt from state and local income tax. That state-tax exemption is why a T-bill can beat a bank account with a slightly higher headline APY in high-tax states.

Does this calculator use current Treasury rates?

No. Rates change at every auction and in the secondary market, so the calculator asks you to enter the discount rate from TreasuryDirect or your brokerage. That keeps the math current without pretending a cached rate is still valid.

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