I Bond Treasury Rate Calculator

The I Bond Treasury Rate Calculator is a free, browser-based tool that turns a Series I savings bond's fixed rate and semiannual inflation rate into its composite rate and projected value. It applies the official Treasury formula, including the 0% composite floor, so you can compare an existing bond against the current issue in seconds.

How Series I Savings Bonds Work

Series I Savings Bonds are inflation-protected U.S. government savings bonds. The Treasury Department combines two rates to determine your yield: a fixed rate that stays the same for the entire 30-year life of the bond, and an inflation rate that resets every 6 months on May 1 and November 1 based on the Consumer Price Index for All Urban Consumers (CPI-U). The composite rate formula is: Composite = Fixed + (2 × Inflation) + (Fixed × Inflation), with a 0% floor on the composite rate (source: TreasuryDirect I bond interest rates).

2026 I Bond Rate History and Outlook

I Bonds reached a peak composite rate of 9.62% in May 2022 due to high inflation, dropping to roughly 4.0-5.3% in 2024 as inflation cooled. The November 2024 issue had a 1.20% fixed rate plus 2.96% inflation rate, for a composite of 5.20%. The May 2025 fixed rate dropped to 1.10%. The current issue, covering purchases from 1 May 2026 through 31 October 2026, pays a 0.90% fixed rate and a 1.67% semiannual inflation rate for a 4.26% composite rate (source: TreasuryDirect I bond interest rates, checked 2026-08-12). The fixed rate is the most valuable component because it persists for the full 30 years, and at 0.90% it sits below the 1.10–1.30% locked in by 2024 and 2025 buyers — if you already hold an older bond, its fixed rate is better than anything on sale today, which is an argument for holding rather than redeeming and rebuying. The next reset takes effect 1 November 2026.

Should You Redeem an Old I Bond and Rebuy at Today's Fixed Rate?

This is the question the rate history above actually raises, and the arithmetic is simpler than it looks because only one of the two components is worth comparing. The inflation half is identical on every I Bond in existence — it resets to the same figure for everyone each May and November — so swapping bonds gains you nothing there. All that changes is the fixed rate, which is locked to the bond for its full 30 years. Today's issue carries a 0.90% fixed rate. Bonds bought in 2024 and 2025 locked 1.10% to 1.30%. Rebuying therefore lowers your permanent yield by 0.2 to 0.4 percentage points, and on top of that you pay two costs: the accrued interest becomes federally taxable in the year you redeem, and the new bond restarts both the 12-month lockout and the 5-year early-redemption penalty window. The trade only makes sense in reverse — when the fixed rate on offer is materially higher than the one on a bond you already hold, which was the case for anyone holding a 0.00% fixed-rate 2021 or 2022 bond when the fixed rate later climbed above 1%. Two practical checks before you act. First, look up your own bond's fixed rate rather than its headline composite, because the composite you see today tells you nothing about what you locked in. Second, if the bond is under five years old, run the three-month interest forfeit through the calculator above before assuming a swap is free. Rates and the reset schedule are published by TreasuryDirect. Updated 2026-08-20.

When to Buy an I Bond: the Rate Reset and the End-of-Month Rule

Two dates decide what an I Bond actually pays you, and neither is the day you decide to buy.

1. The reset date. Rates change on 1 May and 1 November. The next change lands 1 November 2026. Whatever fixed rate is in force on your purchase date is locked to that bond for 30 years, so a purchase on 31 October 2026 locks the 0.90% fixed rate while a purchase on 1 November 2026 locks whatever the Treasury announces that morning.
2. The day of the month. An I Bond earns a full month of interest no matter which day of the month you buy it, and interest is credited on the first of the month. Buying on the 28th rather than the 2nd gives you the same month of interest while keeping your money in your own account for 26 extra days.

Put together, the practical rule is: buy in the last few business days of the month, and if you want to lock the current fixed rate, buy before the reset rather than after it. Allow a couple of business days — a TreasuryDirect purchase submitted on the last day of the month can settle into the next month, which pushes you past a reset you were trying to beat. The purchase-date and interest-accrual rules are set out by TreasuryDirect. Note that a higher composite rate is not by itself a reason to buy: the composite half resets for every holder twice a year, so only the fixed rate is genuinely locked by your timing. Updated 2026-09-06.

I Bond Tax Advantages

I Bonds enjoy three tax breaks. First, federal tax deferral: you don't pay taxes on accrued interest until you redeem the bond (or it matures at 30 years). Second, no state or local income tax — significant for residents of California, New York, New Jersey, Oregon, Hawaii, and other high-tax states. Third, the Education Tax Exclusion: if you use I Bond proceeds to pay qualified education expenses for yourself, your spouse, or your dependent, the interest may be entirely tax-free, subject to modified adjusted gross income phaseouts. The most recent figures published by the IRS are for tax year 2025: the exclusion phases out between $99,500 and $114,500 of MAGI for single filers, and between $149,250 and $179,250 for married filing jointly, disappearing entirely above the top of each band (source: IRS Publication 970). The IRS indexes these bands annually, so confirm the current-year figures before relying on the exclusion. Note also that the bond must be registered in the parent's name, not the child's, for the exclusion to apply. This makes I Bonds particularly powerful for college savings (see also IRS Publication 550).

I Bond Limits and Redemption Rules

Each individual can purchase $10,000 in electronic I Bonds per calendar year through TreasuryDirect, Paper I Bonds bought with a federal tax refund are no longer available — the IRS withdrew that option from 1 January 2025, so every I Bond issued since is electronic. Married couples and businesses with separate EINs can still effectively double or triple the limit. You cannot redeem an I Bond in the first 12 months. Redeeming between months 12-60 forfeits the most recent 3 months of interest. After 5 years, redemption is penalty-free. Bonds stop earning interest after 30 years. Strategy: even if you plan to hold long-term, don't put more than 10% of liquid assets into I Bonds because of the 1-year lockout. Last updated: 2026-09-06.

Why Your Own I Bond Is Not Earning the Headline Rate

Treasury announces a new composite rate twice a year, but that announcement is not the date your bond changes. Each I Bond runs on its own six-month schedule tied to its issue month, so a bond bought in, say, a September starts a fresh rate period every September and March — it keeps the previously announced rate until then and only picks up the new one when its own period turns over. Two people who bought in different months are earning different rates on the same day, and both differ from whatever headline rate is being quoted in the press. Your bond's fixed rate never moves for the life of the bond; only the inflation component reprices. The rate in effect for any individual bond, along with its current value, is shown in your TreasuryDirect account rather than in the announcement.

So read the output above as the rate for a bond whose period is turning over now. To check an existing holding, look up its issue month first and count six-month blocks forward from there.