4-Week T-Bill Calculator
The 4-week T-Bill matures in 28 days and gives you maximum flexibility. Enter your investment amount and current rate to see exactly what you pay, what you earn, and your annual return.
💡 A 4-week T-Bill lets you reinvest every month — making it ideal when interest rates are rising.
This is the amount you get back at maturity. Minimum $100.
Check latest rate → TreasuryDirect.gov
Fixed at 28 days (4 weeks) — auctioned every Tuesday.
How to Calculate 4-Week T-Bill Returns
- Enter your investment amount (face value)
- Apply the discount rate over 28 days
- Calculate the purchase price (face value minus discount)
- Convert your return into an annualized yield
This calculator performs all these steps instantly and shows your exact return.
What is a 4-Week T-Bill?
A 4-week Treasury Bill is the shortest standard T-Bill duration available, maturing in exactly 28 days. It is auctioned every Tuesday by the U.S. Treasury and is one of the most liquid short-term government securities available to individual investors.
Like all T-Bills, the 4-week bill is sold at a discount to its face value. You pay less than face value today and receive the full face value at maturity 28 days later. The difference is your earnings.
How 4-Week T-Bill Returns Are Calculated (Step-by-Step)
The formula (the calculator does this for you):
- Your profit = Investment × Rate ÷ 100 × 28 ÷ 360
- You pay upfront = Investment − Your profit
- Annual return = (Profit ÷ You pay) × (365 ÷ 28) × 100
Step 1 — Your profit:
$10,000 × 4.5% × (28 ÷ 360) = $35.00
Step 2 — What you pay today:
$10,000 − $35.00 = $9,965.00
Step 3 — Your annual return:
($35 ÷ $9,965) × (365 ÷ 28) × 100 = 4.58%
The return is slightly above 4.5% because it is calculated on what you actually paid ($9,965), not the full $10,000. In 28 days, you pocket $35 for doing nothing — and can immediately roll into a new 4-week bill.
Who Should Use the 4-Week T-Bill?
The 4-week T-Bill is best for investors who need maximum flexibility and liquidity. Because it matures every 28 days, you can reassess your options monthly and reinvest at whatever rate the next auction produces.
- Money you may need within the next month
- Investors in rising rate environments — roll over frequently at higher rates
- Businesses parking payroll or operational cash temporarily
- First-time T-Bill investors testing the process with a short commitment
4-Week vs Longer Duration T-Bills
| Duration | Days | Yield (typical) | Liquidity | Best For |
|---|---|---|---|---|
| 4-Week | 28 | Moderate | ⭐⭐⭐⭐⭐ | Max flexibility, rising rates |
| 13-Week | 91 | Moderate-High | ⭐⭐⭐⭐ | 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 is right for you? Read our Best T-Bill Duration Guide for a full breakdown.
Tax Treatment of 4-Week T-Bills
Like all T-Bills, earnings from a 4-week T-Bill are subject to federal income tax but are exempt from state and local taxes. This makes them more attractive than CDs or savings accounts for investors in high-tax states like California, New York, or New Jersey.
See your real after-tax yield based on your federal bracket and state.
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Frequently Asked Questions (FAQ)
Are 4-week T-Bills safe?
Yes, 4-week T-Bills are extremely safe investments backed by the U.S. government. If held to maturity, they guarantee full repayment with no credit risk.
How much can I earn from a 4-week T-Bill?
You can earn around $30 to $40 on a $10,000 4-week T-Bill depending on the rate. The exact return depends on the current discount rate and is paid at maturity.
Why invest in 4-week T-Bills?
4-week T-Bills are ideal for maximum flexibility and short-term cash management. They mature every 28 days, allowing you to reinvest frequently or access your funds quickly.
Are 4-week T-Bills exempt from state tax?
Yes, 4-week T-Bill earnings are exempt from state and local income taxes. You only pay federal tax on the interest earned.