I Bond Calculator

Model a Portfolio of I Bonds

This is a calculator to model a portfolio of Series I Savings Bonds ("I Bonds") over time.

Add Bond Purchases

Instructions for Modeling an I Bond Portfolio

  1. Add an I Bond holding to this form.
    1. Specify the date of purchase in the Date field.
    2. Specify the value of purchase in the Value 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.

The computation engine will generate both a graphical and tabular presentation of the holding's value and performance over time.

Additional Uses for this Tool

ibondcalc.info can backtest portfolios of I Bond holdings.

ibondcalc.info also has a database of historical fixed interest rates as well as their attendant inflation rates according to the United States Bureau of Labor Statistics for each bond issuance. For example, it can model $1,000 of I Bonds purchased in September 1998 to today.

If You are Lost

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):