How to Find the Interest Accrued on an I-Series Bond

by Tim Plaehn, studioD

Series I bonds from the U.S. Treasury earn a variable rate of interest based on the rate of inflation. The Treasury adjusts the current bond interest rate every 6 months, on May 1 and November 1. The rate is based on the consumer price index (CPI). A Series I bond will then earn the new rate for the next 6 months. Since the rate is variable, the future value of an I bond cannot be calculated, but the Treasury provides up-to-date information on the current value of Series I bonds, including interest earned to date.

Locate the savings bond calculator on the Treasury Direct website. Use the Tools tab on the top menu bar to take you to the website section with the calculator. Once on the savings bond calculator page, you must select the "Get Started" link to go to the actual calculator.

Select "Series I" for the bond series and enter the denomination value and issue month of your bond. It is not necessary to enter the serial number.

Click the blue "Calculate" button to show the current value and interest earned on your Series I savings bond. The calculator will show the price of the bond, the total current value, total interest earned and year-to-date interest earned.

Enter the bond information for additional bonds and the calculated values for all of your bonds will remain on the webpage as a list, including bond values and interest earned.


  • Series I savings bond values earn interest and update once a month. All bonds of one denomination issued in a certain month will have the same value.
  • The Treasury website allows you to save your bond values as a webpage to your computer. Use the "View" link to go to a savable webpage. To update, open the page from your computer and select "Return to Savings Bond Calculator." Your bond values will be updated.

About the Author

Tim Plaehn has been writing financial, investment and trading articles and blogs since 2007. His work has appeared online at Seeking Alpha, and various other websites. Plaehn has a bachelor's degree in mathematics from the U.S. Air Force Academy.

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