I Bond Calculator 2026

The I Bond Calculator is a free, browser-based tool that works out what your Series I savings bonds are worth today. Enter the purchase date, amount and rates and it applies the composite-rate formula with semiannual compounding, then subtracts the three-month early-redemption penalty where it still applies, to return your current redemption value.

What Is a Series I Savings Bond?

A Series I Savings Bond is a US Treasury-issued savings bond that earns interest from two components: a fixed rate set at purchase (unchanged for 30 years) and a semiannual inflation rate announced by the Treasury every May and November. The composite rate combines both using the formula: Composite = Fixed + (2 x Inflation) + (Fixed x Inflation). I bonds are backed by the full faith and credit of the US government, exempt from state and local income tax, and can be deferred federally until redemption or maturity at 30 years.

The 2026 purchase limit is $10,000 per Social Security number per year through TreasuryDirect.gov, plus an extra $5,000 in paper bonds via tax refund. I bonds must be held at least 12 months and redeeming before 5 years forfeits the last 3 months of interest. After 5 years, no penalty applies.

How the Composite Rate Works

Because inflation resets every six months, your I bond earning rate changes twice a year on your personal anniversary and six months later. If inflation runs high, your composite rate climbs with it; if inflation falls, your rate falls too. The fixed rate is the portion of the composite rate that stays constant — a higher fixed rate means your real return (return above inflation) is guaranteed. In 2022 the composite rate hit 9.62 percent, driving a surge in I bond purchases; by late 2025 it had normalized closer to 4 percent.

I bond interest compounds semiannually, not annually, so a 4 percent composite rate earns slightly more than a 4 percent simple-interest savings account over the same holding period. This calculator projects value using semiannual compounding and shows the 3-month early-redemption penalty when you exit before year 5.

I Bond vs High-Yield Savings

High-yield savings accounts are fully liquid, FDIC-insured to $250,000, and currently pay 4 to 5 percent APY — but rates drop with Fed cuts. I bonds lock in a portion of return against inflation, exempt you from state tax, and carry a 30-year tax deferral, but charge a 3-month penalty if redeemed within 5 years and cap purchases at $10,000 per year. For short-term emergency savings, high-yield accounts win. For long-term inflation protection and tax efficiency, I bonds are hard to beat.

A common strategy: keep 3 to 6 months of expenses in high-yield savings, and park additional savings into I bonds up to the $10,000 annual limit. Over a decade, a married couple can accumulate $260,000 in inflation-protected Treasury bonds without touching brokerage accounts.

When I Bonds Make Sense

I bonds work best for multi-year savings goals where preserving purchasing power matters more than maximum liquidity. Think: a 5-year home down payment, a college fund, or an inflation-hedged slice of your emergency reserve. They are less useful for very short holding periods (less than 12 months is disallowed entirely) or for investors in 0 percent state-tax states who can get similar yield from high-yield savings with full liquidity. Last updated: April 2026, based on Treasury composite rate formulas and current 2026 tax brackets.

The Best Day of the Month to Buy or Cash In an I Bond

I bond interest is credited by whole month, not by day, and that one rule is worth real money at both ends of the holding period. Buying: a bond earns interest from the first day of the month in which it is issued, so a purchase settled on the 30th earns the same interest for that month as one settled on the 1st. Buying late in the month therefore gets you a full month’s interest for a few days of money — but leave a working-day buffer, because TreasuryDirect can take one to two business days to issue and a purchase that slips past month end loses the whole month. Redeeming: the mirror image applies. You get no credit for a partial month, so cashing out on the 25th earns exactly what cashing out on the 2nd would have. Redeem early in the month, once the month’s interest has posted, rather than sitting on the money for three more weeks for nothing. One more timing point: because interest compounds semiannually, waiting until just after a six-month anniversary rather than just before locks in that compounding step. Confirm dates and current rates on TreasuryDirect’s I bonds page. Updated 2026-09-05.

Why Your TreasuryDirect Balance Looks Lower Than This Calculator

A question that sends people back to Google more than any other: the value shown in your TreasuryDirect account does not match what an I bond calculator says you have earned. Nothing is wrong with either number. During the first five years, an I bond carries a three-month interest penalty on early redemption, and TreasuryDirect displays your balance with that penalty already deducted — it shows what you would walk away with today, not what you have accrued. So a bond held nine months displays roughly six months of interest. Once you cross five years the penalty disappears and the displayed value jumps to the full accrued amount. Two related timing points follow from the same rules. Your bond is completely locked for twelve months — there is no early-withdrawal option at any price, so I bonds are not an emergency fund. And your rate periods run from your purchase month, not from the January and May announcement dates: a bond bought in September moves to the next composite rate the following March, which is why two people holding I bonds at the same moment can be earning different rates. If you are comparing this calculator's output against your account, compare like with like: accrued value here, redemption value there. Redemption rules and rate mechanics are published at TreasuryDirect — Series I savings bonds.

Fixed Rate vs Inflation Rate: Which One Should Decide Your Purchase?

The headline composite rate is the number everyone quotes, and it is the wrong one to buy on if you intend to hold for years. The composite has two parts with very different lifespans. The inflation component resets every six months and is identical for every I bond in existence, whenever it was bought — so it cannot make one purchase date better than another beyond the first six months. The fixed rate is locked at purchase and never changes for the full 30 years, which makes it the only part of the rate that a buying decision can actually influence. Two consequences. First, a bond bought with a 1.2% fixed rate permanently out-earns one bought at 0.0% by 1.2 percentage points a year above inflation, no matter what happens to CPI afterwards. Second, a high advertised composite rate driven purely by a temporary inflation spike is not a reason to rush a purchase, while a rise in the fixed rate at the May or November reset genuinely is. When comparing two purchase dates in the calculator above, compare the fixed rates first and treat the inflation component as noise. Updated 2026-09-05.