I Bond Calculator 2026 — What Your I Bonds Are Worth by Issue Date

Pick the month your I bond was issued and the month you want it valued, and the calculator works out what Treasury will pay, to the cent. It does not assume one rate for the whole term: every I bond keeps the fixed rate of the six-month window it was bought in, and its inflation part changes every six months from the issue month. An I bond bought between May 1 and October 31, 2026 starts at a 4.26% composite rate, a 0.90% fixed rate plus a 1.67% inflation rate for six months.

Treasury's rules are applied exactly as written in 31 CFR part 359. Each six-month period of your bond, counted from its issue month, earns fixed rate + 2 × the semiannual inflation rate + fixed rate × inflation rate, rounded to 0.01% and never below zero, using the inflation rate announced most recently when that period began. Interest is added on the first of each month and compounds every six months, and every step is rounded to the cent on a $25 unit, as Treasury does. Cashed before five years, a bond is worth what it was worth three months earlier; in its first 12 months it cannot be cashed at all. Checked against Treasury's published value tables, the results match every I bond issue month since September 1998 to the cent.

The table below the calculator shows what $1,000 of I bonds is worth this month for each rate window since the first bonds were sold in 1998, with the fixed rate each window locked in. The fixed rate is what separates them: bonds bought from September 1998 to October 2000 carry 3.30% to 3.60% on top of inflation for life, while bonds bought from May 2008 to October 2022 carry between 0% and 0.70%, most of them 0%. For a date after the latest announcement, the calculator assumes the current 1.67% inflation rate continues and marks the value as a projection; Treasury sets new rates every May 1 and November 1. Interest stops after 30 years, and it is exempt from state and local tax but federally taxable when you cash the bond.