Why Use This I Bond Calculator
Series I Savings Bonds are a popular inflation-protected investment backed by the U.S. government. Our I Bond Calculator helps you:
- 💰 Calculate Current Value — know exactly what your I Bond is worth today.
- 📈 Track Interest Growth — see how much interest your bond has earned.
- 🔄 Understand Composite Rates — see how fixed and inflation rates combine.
- 📊 Visualize Growth — watch your bond’s value grow over time.
- 🔒 100% Private — all calculations run locally in your browser.
What Is a Series I Savings Bond?
A Series I Savings Bond (I Bond) is a U.S. government savings bond that earns interest based on two components:
| Component | Description |
|---|---|
| Fixed Rate | Set at purchase and locked for the life of the bond (up to 30 years). |
| Inflation Rate | Adjusted twice a year (May 1 and November 1) based on the CPI. |
The combination of these two rates creates the composite rate — the actual interest your bond earns.
The I Bond Composite Rate Formula
The composite rate is calculated using this formula:
Composite Rate = [Fixed Rate + (2 × Semiannual Inflation Rate) + (Fixed Rate × Semiannual Inflation Rate)]
Example:
| Variable | Value |
|---|---|
| Fixed Rate | 0.90% |
| Semiannual Inflation Rate | 1.68% |
| Composite Rate | [0.0090 + (2 × 0.0168) + (0.0090 × 0.0168)] = 4.26% |
Current I Bond Rates (May 2026)
| Rate Type | Current Rate |
|---|---|
| Composite Rate | 4.26% |
| Fixed Rate | 0.90% |
| Semiannual Inflation Rate | 1.68% |
| Effective Period | May 1, 2026 – October 31, 2026 |
How I Bond Interest Works
- Interest is compounded semiannually — the composite rate is applied to your bond’s value every six months.
- The fixed rate stays the same — it’s locked for the life of the bond (up to 30 years).
- The inflation rate changes — every May and November based on CPI data.
- Interest is added to the bond’s value — you earn interest on interest (compounding).
- Penalty for early redemption — if you redeem within 5 years, you forfeit the last 3 months of interest.
How to Use This I Bond Calculator
- Select your purchase date — use the calendar picker to select when you bought your I Bond.
- Enter your purchase amount — how much you invested (minimum $25).
- Enter the fixed rate — the fixed rate in effect when you purchased your bond.
- Enter the semiannual inflation rate — the current inflation rate (check TreasuryDirect).
- View your results — see your bond’s current value, total interest, and composite rate.
The tool updates instantly as you adjust any input — no “Calculate” button required.
I Bond Interest Rate History
| Effective Date | Fixed Rate | Inflation Rate | Composite Rate |
|---|---|---|---|
| May 2026 | 0.90% | 1.68% | 4.26% |
| Nov 2025 | 0.90% | 1.56% | 4.03% |
| May 2025 | 0.00% | 1.69% | 3.38% |
| Nov 2024 | 0.00% | 1.24% | 2.48% |
| May 2024 | 0.00% | 1.82% | 3.64% |
I Bond Calculator Frequently Asked Questions
What is an I Bond?
A Series I Savings Bond (I Bond) is a U.S. government savings bond designed to protect your savings from inflation. It earns interest based on a fixed rate plus an inflation-adjusted rate that changes every six months.
How is the I Bond composite rate calculated?
The composite rate is calculated using the formula: Composite Rate = [Fixed Rate + (2 × Semiannual Inflation Rate) + (Fixed Rate × Semiannual Inflation Rate)].
What is the current I Bond rate?
As of May 2026, the composite rate is 4.26% with a 0.90% fixed rate for bonds purchased through October 2026.
When do I Bond rates change?
I Bond inflation rates change twice a year — on May 1 and November 1 — based on the Consumer Price Index (CPI).
How often does interest compound on I Bonds?
I Bond interest is compounded semiannually. The composite rate is applied to the bond’s value every six months.