I-Bond Calculator (Series I Savings Bonds)
Calculate Series I Savings Bond value with current composite rate. See early redemption penalty and year-by-year growth.
By Konstantin Iakovlev · Updated April 2026 · Source: SEC
Value at Maturity
$12,346.20
Total Interest
$2,346.20
Effective Annual Return
4.31%
I Bond Summary
| Purchase Amount | $10,000.00 |
| Value Before Penalty | $12,346.20 |
| Final Value | $12,346.20 |
| Total Interest Earned | $2,346.20 |
| Effective Annual Return | 4.31% |
Use the I-Bond Calculator (Series I Savings Bonds) above to calculate your results. Enter your values and see instant results — all calculations run in your browser.
Disclaimer: This calculator is for informational purposes only and does not constitute tax, financial, or legal advice. Results are estimates based on the information you provide and current rates. Always consult a qualified tax professional or financial advisor for advice specific to your situation.
How It Works
Series I Savings Bonds grow on a rate that shifts with inflation, which makes their future value harder to eyeball than a fixed-rate investment. This calculator works it out for you, applying the current composite rate and showing the value building year over year so you can plan around it and see what an early cash-out would cost. Buy an I-Bond in early 2026, for instance, and its opening composite rate will reflect the inflation and fixed rates in effect at that moment.
Valuation proceeds semi-annually from the bond's issue date. Each period the composite rate is applied, that rate being the fixed rate locked in at purchase combined with the semiannual inflation rate, which the Treasury resets every six months. If you redeem inside the first five years, three months of interest is subtracted to reflect the early redemption penalty. Accrual continues for up to 30 years, or until you cash the bond in, whichever comes first.
A few features shape the outcome. Interest is tax-deferred, so you owe nothing on it until you redeem the bond or it matures. The three-month interest penalty on redemptions before five years is easy to overlook, but it is built into the figures here. And while the inflation component moves with each adjustment, the fixed rate set on the day you buy stays put for the life of the bond, steadily anchoring its growth.
Example: $10,000 I-Bond Purchased in January 2026
- 1 Input: Purchase Amount = $10,000; Purchase Date = January 2026; Holding Period = 3 years; Assumed Fixed Rate (for 2026) = 1.30%; Assumed Annual Inflation Rate (for 2026-2029) = 3.20%
- 2 Calculation: The calculator first determines the initial composite rate (Fixed Rate + 2 * Semiannual Inflation Rate). For a 1.30% fixed rate and 3.20% annual inflation, the initial composite rate would be 1.30% + (2 * (3.20% / 2)) = 4.50%. This rate is applied semi-annually. After 3 years, the accrued interest is calculated, and then three months of interest are subtracted for the early redemption penalty.
- 3 Intermediate Result: After 3 years, the bond's value before penalty is approximately $11,424. The interest accrued in the final three months of the holding period is roughly $120.
- 4 Final Result: After applying the early redemption penalty, the estimated redemption value of your $10,000 I-Bond purchased in January 2026 after 3 years would be approximately $11,304.
Source: SEC · Last updated: April 2026
Frequently Asked Questions
What is the current I-Bond rate for 2026?
How much can I buy in I-Bonds per year?
When can I cash in my I-Bonds without penalty?
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