Savings Bond Calculator

Frequently asked questions

Why build another I bond calculator when TreasuryDirect already has one?

TreasuryDirect's own Savings Bond Calculator is the authoritative source and exact for paper bonds, but it's built around entering a serial number and denomination one bond at a time, with a dated interface that many people find slow to use for checking several bonds at once. This tool skips the serial number (you don't need it for a value estimate, just the issue month and amount) and lets you track every bond you own in one list, so you can see your total I bond position, not just one bond at a time.

Where does the rate data come from?

TreasuryDirect's own published I Bond Rate History, the same fixed-rate and semiannual inflation-rate figures the Treasury itself announces every May 1 and November 1, sourced directly from their published spreadsheet rather than recomputed or estimated by this site.

Why do I need the issue month instead of just the purchase date?

Because that's what actually determines an I bond's rate. The fixed rate an I bond earns is locked in for its entire life based on the 6-month window it was first issued in, and its inflation-linked portion resets every 6 months from that same issue-month anniversary. Two bonds bought a day apart, one at the end of April and one at the start of May, can lock in meaningfully different fixed rates, because they fall in different 6-month issuance windows.

What is the composite rate and how is it calculated?

It's the combined interest rate an I bond earns in a given 6-month period: fixed rate + (2 x semiannual inflation rate) + (fixed rate x semiannual inflation rate), the Treasury's own published formula. The fixed rate stays constant for the bond's life; the inflation rate resets every 6 months based on the most recently published CPI-based figure, so a bond's composite rate can and does change every 6 months even though nothing about the bond itself changed.

Why does the tool show two different values?

Accrued value is everything the bond has actually earned. Redeemable value is what you'd actually receive if you cashed it out today, which matters because I bonds held less than 5 years forfeit their last 3 months of interest as an early-redemption penalty. Bonds held under 12 months can't be redeemed at all, by law, so no redeemable figure is shown for those.

Is this exact to the penny?

It's built on the Treasury's real published rates and their own documented compounding method (monthly interest accrual within each 6-month period, compounding at the 6-month mark), so it should track official redemption-value tables closely. It isn't pulling your bond's actual serial-number record from TreasuryDirect, so treat it as a reliable estimate for planning, and check your TreasuryDirect account or the official calculator for the figure that matters for a real transaction.

Is my bond information private?

Yes. Every bond you add is stored in this browser's own IndexedDB, on your device, and never sent anywhere, not even a serial number is asked for. There's no account and no bank or TreasuryDirect login, so clearing your browser data or switching devices starts you over.