13-Week T-Bill Calculator
Calculate the exact purchase price, earnings, and annualized yield for a 13-week (91-day) Treasury Bill. The duration is fixed at 91 days — just enter your face value and current discount rate.
Minimum $100 — T-Bills are sold in $100 increments on TreasuryDirect.
Use the latest 13-week T-Bill auction rate from TreasuryDirect.gov.
Fixed at 91 days (13 weeks) — auctioned every Monday.
What is a 13-Week T-Bill?
A 13-week Treasury Bill is a short-term U.S. government security that matures in 91 days (approximately 3 months). It is auctioned every Monday by the U.S. Treasury and is one of the most popular T-Bill durations for individual investors — offering a balance of competitive yield and quarterly liquidity.
Like all T-Bills, you buy it at a discount to face value and receive the full face value at maturity. The difference is your earnings — guaranteed by the U.S. government.
13-Week T-Bill Formula
- Discount = Face Value × (Discount Rate / 100) × (91 / 360)
- Purchase Price = Face Value − Discount
- Annualized Yield = (Discount / Purchase Price) × (365 / 91) × 100
Face Value: $10,000 | Duration: 91 days
Discount = $10,000 × 4.5% × (91/360) = $113.75
Purchase Price = $10,000 − $113.75 = $9,886.25
Annualized Yield = ($113.75 / $9,886.25) × (365/91) × 100 = ~4.63%
Who Should Use the 13-Week T-Bill?
The 13-week T-Bill is widely considered the best starting point for first-time T-Bill investors. It is short enough to feel comfortable, matures quarterly for easy planning, and offers a competitive yield close to longer-duration T-Bills.
- First-time T-Bill investors wanting a short first commitment
- Investors who review their cash position quarterly
- People in rising rate environments — reinvest at higher rates every 3 months
- Aligning with quarterly estimated tax payments or financial planning
13-Week vs Other T-Bill Durations
| Duration | Days | Yield (typical) | Liquidity | Best For |
|---|---|---|---|---|
| 4-Week | 28 | Moderate | ⭐⭐⭐⭐⭐ | Max flexibility |
| 13-Week | 91 | Moderate-High | ⭐⭐⭐⭐ | Beginners, quarterly planning |
| 26-Week | 182 | High | ⭐⭐⭐ | Best balance — most popular |
| 52-Week | 364 | Highest (normal) | ⭐⭐ | Lock in rate for a year |
Not sure which duration fits your situation? Read our Best T-Bill Duration Guide for a full breakdown including how the rate environment affects your choice.
Tax Treatment of 13-Week T-Bills
Earnings from 13-week T-Bills are subject to federal income tax but are exempt from state and local taxes by federal law. This tax advantage makes T-Bills more attractive than CDs or savings accounts for investors in high state-tax states like California, New York, Oregon, or New Jersey.
Find your real after-tax yield and the CD rate needed to match your T-Bill.
Rolling Over Your 13-Week T-Bill
When your 13-week T-Bill matures, you can reinvest the full face value into a new one — this is called rolling over. On TreasuryDirect, you can enable auto-reinvestment so the rollover happens automatically with no action required.
Rolling over four times gives you a full year of T-Bill returns with quarterly compounding. Use our reinvestment calculator to see exactly how much you earn across multiple rollovers.
See how much you earn rolling over your 13-week T-Bill quarterly for 1–5 years.
Frequently Asked Questions
Is a 13-week T-Bill safe?
Yes — 13-week T-Bills are short-term U.S. government securities backed by the full faith and credit of the United States. They are considered risk-free if held to maturity. Your principal is 100% guaranteed.
How much does a 13-week T-Bill pay?
At a 4.5% discount rate, a $10,000 13-week T-Bill earns approximately $113.75 over 91 days, with an annualized yield of about 4.63%. The earnings are paid as a lump sum when the T-Bill matures.
Who should invest in 13-week T-Bills?
13-week T-Bills are ideal for beginners and investors who want quarterly liquidity. They are also a good choice when interest rates are rising — maturing every 3 months lets you reinvest at progressively higher rates.
How often are 13-week T-Bills auctioned?
13-week T-Bills are auctioned every Monday by the U.S. Treasury. Results are published the same day. You can purchase them through TreasuryDirect.gov or any major brokerage like Fidelity or Schwab.
Related Calculators
New to T-Bills? What Are Treasury Bills — Complete Guide · Are T-Bills Worth It? · Best T-Bill Duration Guide