T-Bill Reinvestment Calculator
Most T-Bill investors don't cash out — they roll over (reinvest) at maturity. See how your money grows when you keep reinvesting your T-Bill earnings over time.
TreasuryDirect minimum is $100 (in $100 increments). Most brokerages require $1,000.
Assumed constant across all rollovers. Check TreasuryDirect.gov for current rates.
This determines how many times you can reinvest within your chosen period.
How long you plan to keep rolling over your T-Bills.
Not sure? Use your marginal (top) bracket from your last tax return. T-Bills are exempt from state tax.
What is T-Bill Reinvestment (Rolling Over)?
When a T-Bill matures, instead of taking the cash, most investors immediately buy a new T-Bill — this is called rolling over or reinvesting. Because you now have slightly more money (your original investment plus the discount earned), your next T-Bill earns a little more. Over time, this compounding effect meaningfully increases your total returns.
How the Reinvestment Calculation Works
- Rollover 1: Buy T-Bill at purchase price, receive face value at maturity
- Rollover 2: Reinvest full face value as the new face value
- Each rollover: Earnings = Face Value × (Rate / 100) × (Days / 360)
- Compounding: Each rollover's face value = previous face value + earnings
Why Rolling Over T-Bills Makes Sense
A single 6-month T-Bill at 5% earns a certain amount. But if you roll it over twice in a year, the second T-Bill earns interest on a slightly larger amount — giving you a higher effective annual yield than the stated discount rate. This is the power of compounding with T-Bills.
T-Bill Ladder vs Simple Rollover
A simple rollover puts all your money in one T-Bill at a time. A T-Bill ladder splits your money across multiple T-Bills of different durations so that one always matures every few weeks, giving you regular access to cash. Use our Ladder Strategy Calculator for that approach.
Related Calculators
Learn more: What Are Treasury Bills — Complete Guide · Best T-Bill Duration Guide · Are T-Bills Worth It?
Frequently Asked Questions
What does rolling over a T-Bill mean?
Rolling over means reinvesting your T-Bill at maturity into a new T-Bill of the same duration instead of taking the cash. On TreasuryDirect, you can set up automatic reinvestment so your T-Bill rolls over without any manual action required.
How does compounding work with T-Bills?
T-Bills do not compound in the traditional sense — they pay a lump sum at maturity. However, when you roll over, your new face value equals your previous face value plus earnings, so each subsequent T-Bill earns slightly more than the last. Over multiple rollovers, this produces a meaningful compounding effect.
Is it better to roll over short-term or long-term T-Bills?
It depends on the rate environment. In rising rate periods, roll over short-term T-Bills (4-week or 13-week) frequently to capture higher rates. In falling rate periods, lock into longer durations (26-week or 52-week) to preserve today's higher yield before rates drop.
How much more do I earn by reinvesting vs cashing out?
On a $10,000 investment at 4.5% over 1 year with quarterly rollovers, reinvesting earns approximately $460 vs $450 if you just held one 52-week T-Bill. The difference grows significantly over 2–5 years due to compounding.