I-Bond Real Yield Calculator
Calculate Series I Savings Bond real return after inflation and taxes.
Compare I-Bond yield to TIPS, Treasuries, and HYSA for inflation-protected income.
Series I Savings Bond (I-Bond)
I-Bonds combine a fixed real rate with inflation protection. The composite rate adjusts every 6 months based on CPI-U.
The composite rate formula: Composite = Fixed rate + 2 × Inflation rate + (Fixed × Inflation)
For practical purposes the cross-product is small: Composite ≈ Fixed rate + 2 × Inflation rate
Where inflation rate is 6-month CPI-U change, not annualized. The 2× factor in the formula effectively annualizes it.
Recent fixed rates (set by Treasury, semi-annually):
| Period | Fixed Rate |
|---|---|
| Nov 2024 - Apr 2025 | 1.20% |
| May 2024 - Oct 2024 | 1.30% |
| Nov 2023 - Apr 2024 | 1.30% |
| May 2023 - Oct 2023 | 0.90% |
| Nov 2022 - Apr 2023 | 0.40% |
| Older periods | 0.00% to 3.40% |
Composite rate examples:
- May 2022 - Oct 2022: 9.62% (record-high inflation)
- May 2024 - Oct 2024: 4.28%
- Nov 2024: 3.11%
I-Bond rules:
- Purchase limit: $10,000/year per person via TreasuryDirect ($5,000 extra paper via tax refund)
- Hold time: 1 year minimum (cannot redeem at all in first 12 months)
- Early redemption penalty: lose last 3 months of interest if redeemed in years 2-5
- Maximum hold: 30 years
- Tax treatment: federal tax only (NO state tax), tax-deferred until redemption
- Education exclusion: I-Bond interest tax-free if used for qualified higher education
I-Bonds vs alternatives:
| Investment | Yield (typical) | Inflation Protection | Risk |
|---|---|---|---|
| I-Bond | ~3-5% | YES (CPI-linked) | Government |
| TIPS | ~2-3% real + CPI | YES | Government |
| HYSA | ~4-5% | NO | FDIC-insured |
| 10-year Treasury | ~4-5% nominal | NO | Government |
| Money Market | ~4-5% | Partial | Sweep risk |
| Series EE | ~2-3% | NO (but doubles in 20 years) | Government |
When I-Bonds win:
- High inflation periods (2021-2023 sweet spot)
- Long-term emergency fund parking (after 1-year lockup)
- Tax-deferred income for high earners (no state tax)
- Education savings (tax-free if qualified)
When other instruments win:
- Need liquidity (HYSA wins — no lockup)
- Low inflation environment (TIPS or Treasuries with higher fixed rates win)
- Already maxed at $10K/year (must use other instruments)
- Don’t want TreasuryDirect hassle (their UX is famously bad)
The “30-month flip” strategy: Some investors hold I-Bonds for exactly 30 months: get 27 months of interest, lose 3-month penalty. Maximizes inflation hedge while keeping average duration short.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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