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% |
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.
Is my data stored anywhere?
No. All calculations run locally in your browser. No data is sent to any server.