Not affiliated with the U.S. Treasury, TreasuryDirect or BLS.
About this I bond calculator
Who makes it
plusbeauxjours builds small, free tools that answer one question clearly, with sources. This one answers: if I buy I bonds in October 2026 instead of waiting for November, which comes out ahead, by how much, and what decides it? It also works out what an I bond you already own is worth. See all our tools (opens in a new tab).
Not affiliated
We are not affiliated with the U.S. Treasury, TreasuryDirect, the Bureau of the Fiscal Service or the Bureau of Labor Statistics. We use their published rules and data. To buy or cash in I bonds, use TreasuryDirect directly.
Your privacy
Everything is calculated in your browser. Nothing you type is sent anywhere, and nothing is ever put in the page address. If you want, your entries are remembered on this device only; the “Clear my entries” button removes them. We use Google Analytics to count visits, without anything you type. There are no ads and no affiliate links.
What it is and isn't
An estimate for education. It follows TreasuryDirect's published method (31 CFR 359) and matches its calculator to the cent for past dates. The November fixed rate and future inflation are assumptions until Treasury announces them, and we never predict the fixed rate. This is not financial or tax advice.
Questions about how the numbers work? Read how it works. Legal: Privacy (opens in a new tab) and Terms (opens in a new tab).
Last checked .