Savings Bond Calculator
Calculate the future value of a savings bond. Enter principal, annual rate and years to see what your bond grows to and the total interest earned, compounded yearly.
Updated 2026-06-14 · Free · No sign-up · Runs privately in your browser
Show the formula & steps
How the Savings Bond Calculator Works
A savings bond is a loan you make to a government or issuer that pays you back with interest over time. This calculator shows what a bond is worth after a holding period by applying annual compound interest to your starting amount. Enter the principal you paid, the annual interest rate, and the number of years you have held the bond. The tool instantly returns the future value and the total interest you have earned.
The Formula
Future value = principal × (1 + annual rate)^years
Here the annual rate is written as a decimal (4.3% becomes 0.043). Each year, the balance is multiplied by (1 + rate), so interest earns interest — the hallmark of compounding.
To find just the interest you have earned, subtract your original principal:
Interest earned = future value − principal
Worked Example
Suppose you bought a bond for $1,000 at a 4.3% annual rate and held it for 20 years:
- Future value = $1,000 × (1 + 0.043)^20
- (1.043)^20 ≈ 2.3211
- Future value ≈ $1,000 × 2.3211 = $2,321.06
- Interest earned = $2,321.06 − $1,000 = $1,321.06
Over 20 years, the bond more than doubled — a clear illustration of why time is the most powerful ingredient in compound growth.
Compounding Over Time
The longer you hold a bond, the more dramatically compounding works in your favor. The table below shows how a $1,000 principal at a 4.3% annual rate grows:
| Years held | Future value | Interest earned |
|---|---|---|
| 5 | ≈ $1,234 | ≈ $234 |
| 10 | ≈ $1,524 | ≈ $524 |
| 20 | ≈ $2,321 | ≈ $1,321 |
| 30 | ≈ $3,536 | ≈ $2,536 |
A Note on Real Savings Bonds
This tool uses a clean annual compounding model so you can quickly project growth at any fixed rate. Actual U.S. Treasury savings bonds work slightly differently: Series EE bonds compound semiannually at a fixed rate (with a guarantee to double in 20 years), while Series I bonds combine a fixed rate with an inflation-adjusted rate that changes twice a year. For an exact redemption value of a paper or electronic Treasury bond, use the official TreasuryDirect calculator and your bond’s issue date — but for planning and estimates, this calculator gives a reliable picture.
Frequently asked questions
How do I calculate the value of a savings bond?+
Multiply the principal by (1 + the annual rate) raised to the number of years held. For example, $1,000 at 4.3% for 20 years grows to $1,000 × (1.043)^20 ≈ $2,321. The interest earned is the future value minus the original principal.
How is savings bond interest compounded?+
This calculator assumes interest compounds annually, meaning each year's interest is added to the balance and earns interest the following year. Real U.S. Treasury savings bonds (Series EE and I) compound semiannually and may carry variable rates, so treat this as a close estimate.
What is the difference between simple and compound interest on a bond?+
Simple interest pays only on the original principal each period. Compound interest pays on the principal plus all previously earned interest, so the balance grows faster over time. Savings bonds use compounding, which is why long holding periods produce outsized growth.
How long does it take a savings bond to mature?+
Series EE and I U.S. savings bonds earn interest for up to 30 years. Series EE bonds are guaranteed to at least double in value if held 20 years. Use this calculator with your bond's rate and the number of years held to estimate its current worth.
Will I pay tax on savings bond interest?+
Interest on U.S. savings bonds is exempt from state and local tax but subject to federal income tax. You can report the interest each year or defer it until you cash the bond or it matures. Education-related redemptions may qualify for a federal tax exclusion.