Model a Portfolio of I Bonds

Use this calculator to see how your Series I Savings Bonds ("I Bonds") have grown, month by month.

Instructions for Modeling an I Bond Portfolio

1. Add an I Bond holding to this form.
   1. Enter the date you bought the bond in the Issue Date field.
   2. Enter the amount you paid in the Purchase Amount field.
2. If you have more than one holding, press Add row to add another row for your holding. Repeat the previous steps for that holding.
3. When you are done, press Compute.

You'll get a chart and a month-by-month table of each purchase's value.

Additional Uses for this Tool

This site can also backtest portfolios of I Bond holdings.

It also has a table of every I Bond fixed rate and semiannual inflation rate announced by the U.S. Treasury (the inflation rate is based on the CPI-U, published by the Bureau of Labor Statistics). For example, it can model $1,000 of I Bonds purchased in September 1998 to today.

New to I Bonds?

If you are brand new to I Bonds and don't know what they are, consult the Bogleheads' resources. They have a wealth of information, including an article on I Bonds. You may find I Bonds useful for the following purposes (not exhaustive):

• Holding the top end of a large emergency fund (you can't redeem an I Bond in its first 12 months, and before 5 years you give up the last 3 months of interest)
• Tax-advantaged savings (interest is free of state and local income tax, and federal tax can wait until you redeem)