Bid Rate Calculator
Treasury bill quotes look like a foreign language the first time you see them: a “4.30% discount rate” on a 13-week bill is not the interest you earn, it is a quoting convention built on face value and a 360-day year. The number that matters, what you actually pay and what you actually earn, takes one formula to uncover, and most quote pages never show it.
The Bid Rate Calculator below converts an auction discount rate into the real economics: the price per $100, your purchase price, the interest you earn at maturity, and the investment yield you can compare against a CD or savings account. It uses the Treasury’s own formulas, including the separate treatment for bills longer than a half-year.
Quick Answer
Key takeaways
- Price per $100 = 100 × (1 − discount rate × days ÷ 360), per 31 CFR 356, Appendix B.
- The investment yield (bond-equivalent) is always higher than the discount rate. Use it to compare with CDs and savings.
- Bills longer than a half-year use a different yield formula (a quadratic), which this calculator applies automatically.
- T-bill interest is federally taxable but exempt from all state and local income tax.
Discount rate vs. investment yield
The discount rate quoted at auction is computed on the bill's face value with a 360-day year: discount = (face − price) ÷ face × (360 ÷ days). The investment yield, also called the coupon-equivalent or bond-equivalent yield, is computed on the price you actually pay with a 365-day year: yield = (face − price) ÷ price × (365 ÷ days). Because it divides by the smaller price and annualizes over more days, the investment yield is always higher than the discount rate. A 4.30% discount rate on a 91-day bill is a 4.408% investment yield.
That difference is the whole reason the two numbers exist. The discount rate is the auction's quoting language; the investment yield is the comparison language. When you weigh a T-bill against a high-yield savings account or a CD, the investment yield is the number on the same scale. Treasury bills come in 4, 8, 13, 17, 26, and 52-week terms, cost a minimum of $100 in $100 increments at TreasuryDirect, and pay no periodic coupons: the discount is the interest, realized in one payment at maturity.
Worked example, checked against this exact tool
Enter the pre-filled defaults ($10,000 face, 4.30% discount rate, 13-week term) and click Calculate:
| Figure | Value |
|---|---|
| Price per $100 | 98.913056 (100 × (1 − 0.043 × 91 ÷ 360)) |
| Purchase price | $9,891.31 |
| Interest at maturity | $108.69 (10,000 − 9,891.31) |
| Investment yield | 4.408% |
Switch to the 52-week term with the same rate: the price falls to $9,565.22, interest rises to $434.78, and the calculator switches to the long-bill quadratic for the yield. Same rate, very different economics, which is why the term selector matters. When comparing short-term parking options, run the after-tax yield against your savings account APY before you decide.
The tax edge most comparisons forget
T-bill interest is subject to federal income tax but exempt from all state and local income taxes, per IRS Publication 550 and TreasuryDirect. In a high-tax state, that exemption is worth real money: a 4.408% T-bill yield in a state with a 9% income tax is equivalent to roughly a 4.84% fully-taxable yield (4.408 ÷ (1 − 0.09)). You report the interest in the year the bill matures, and you should receive a Form 1099-INT. If you are comparing a T-bill against a CD, adjust the CD's yield down by your state tax rate first, then compare.
What competing T-bill calculators miss
We checked the popular Treasury bill tools. Three gaps stood out.
Discount rate presented as yield. Several tools echo the auction rate back as "your rate," which understates the return. This page computes the investment yield on every result and labels which number is which.
One formula for all terms. Most calculators apply the short-bill formula to 52-week bills, where Treasury's own rules require the coupon-equivalent quadratic. This one switches formulas at the half-year mark automatically.
No tax context. The state-tax exemption is the T-bill's quiet superpower against CDs, and competitors rarely mention it. The equivalence math above turns it into a number you can compare.
Frequently asked questions
Price per $100 = 100 × (1 − discount rate × days to maturity ÷ 360), per 31 CFR 356, Appendix B. A 91-day bill at 4.30% costs 98.913056 per $100, so a $10,000 bill costs $9,891.31. Multiply by face ÷ 100 for any face value.
The discount rate is based on face value and a 360-day year; the investment (bond-equivalent) rate is based on the price you actually pay and a 365-day year. The investment rate is always higher. Use the investment rate to compare a T-bill with a CD or savings account.
For bills of not more than a half-year, Treasury uses the simple bond-equivalent formula. For longer bills it assumes a coupon bond would have paid a half-year coupon and solves a quadratic for the yield. This calculator applies the correct formula for each term automatically.
Federal yes, state and local no. T-bill interest is subject to federal income tax but exempt from all state and local income taxes (IRS Publication 550; TreasuryDirect). You report it in the year the bill matures and should receive Form 1099-INT.
$100, in increments of $100, bought at TreasuryDirect or through a broker. The maximum is $10 million per auction with a non-competitive bid.
4, 8, 13, 17, 26, and 52 weeks, auctioned regularly at TreasuryDirect. Unlike bonds or CDs, T-bills pay no periodic coupons: you buy at a discount and receive face value at maturity, and the difference is your interest.
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References
- Nasdaq, "How to Calculate the Price of Treasury Bills" - price from the discount rate with a 360-day year, the $1,000/180-day/1.5% worked example, and the discount-as-interest explanation. Nasdaq: How to Calculate the Price of Treasury Bills. Accessed October 19, 2026.
- Microsoft Learn, "WorksheetFunction.TBillPrice method" - documents the Treasury price formula with DSM (days settlement to maturity) and the 31 CFR 356, Appendix B basis used by Excel's TBILLPRICE. Microsoft Learn: TBillPrice Method. Accessed October 19, 2026.
- TeamzLab, "Treasury Bill Calculator" - 91-day worked example at 4.30%: $9,891.31 price, $108.69 interest, 4.408% investment yield, plus the federal-taxable/state-exempt treatment. TeamzLab: Treasury Bill Calculator. Accessed October 19, 2026.
- FreeFastCalculator, "Treasury Bill Calculator: T-Bill Price and Yield" - discount vs. investment rate distinction, the half-year formula split, and the $100 minimum in $100 increments at TreasuryDirect. FreeFastCalculator: Treasury Bill Calculator. Accessed October 19, 2026.