Series I savings bonds protect your cash from inflation and are backed by the U.S.
I Bond Calculator
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Treasury. I bonds issued from November 2026 through April 2027 earn a 5.51% composite rate: a 1.40% fixed rate that lasts for the bond’s life plus an inflation rate that resets every six months. This calculator shows what a bond could be worth, the penalty for cashing out early, and how it stacks up against a CD or Treasury bill.
I bond rules to know
- Purchase limit: $10,000 per person per calendar year in electronic bonds at TreasuryDirect.gov, plus up to $5,000 in paper bonds through a federal tax refund.
- 12-month lockup: you can’t cash an I bond in its first year.
- Early-redemption penalty: cash out before five years and you lose the last three months of interest.
- Tax perks: interest is exempt from state and local income tax, and you can defer federal tax until you redeem.
Frequently asked questions
How is the composite rate calculated?
Composite rate = fixed rate + (2 × semiannual inflation rate) + (fixed rate × semiannual inflation rate). With a 1.40% fixed rate and 2.04% semiannual inflation, that’s 5.51%.
Will I really earn 5.51% the whole time?
Only the fixed part is locked in. The inflation part changes every May and November based on the Consumer Price Index, so the calculator’s projection assumes today’s rate continues.
Related: TIPS vs. I Bonds, Best CD Rates, CD Calculator.
Source: TreasuryDirect I bond rates for bonds issued November 2026–April 2027 (fixed 1.40%, semiannual inflation 2.04%). Rates as of November 2026.