Press Enter to search or ESC to close
Finance

How to Calculate I Bonds

Patrick Harwood
· · Updated Jan 16, 2026 · 3 min read
Series I savings bonds are a popular alternative to the traditional Series EE bond. Like EE bonds, I bonds are available in paper form at banks and other financial institutions or as "electronic bonds" online. What makes I bonds distinctive is that they are linked to inflation.

This means that the interest rate is adjusted periodically (every 6 months) to offset inflation. I bonds are sold at face value starting at $25 and may be purchased by anyone with a Social Security number. Interest is added monthly to the principal of the bond.

 

Things You'll Need

  • I bond purchase date
  • Inflation rate history
  • Serial number
  • Calculator
 

5 Steps To Calculate I Bonds

How to Calculate I Bonds

 

1. Find The Fixed Rate Of The Bond

I bonds have a composite rate consisting of a fixed rate set when the bond is issued (purchased) and an inflation rate that is adjusted semi-annually. To locate the fixed rate for a particular I bond, check the rate history table published online.

2. Determine The İnitial İnflation İnterest Rate

A complete inflation rate history table accompanies the fixed rate table at Treasury Direct. Multiply the listed (semi-annual) rate by two to find the annual rate and add it to the bond's fixed rate. This is the composite rate in effect when the I bond was purchased.

For example, if the fixed rate is 1.40 percent and the semi-annual rate is 1.20 percent, the composite rate is 1.40 + (2 x 1.10), or 3.60 percent.

 

3. Divide The Composite Rate By 12 To Find The Monthly Periodic Rate

If the composite rate is 3.60 percent, this is 3.60/12 equals 0.30 percent. Interest on I bonds is calculated and added to the principal monthly, so multiply the principal (this initially is the face value) by the monthly periodic rate and add the result to the principal to find the value of the I bond.

 

4. Repeat Step 3 For Each Month The İnflation Rate Remained Unchanged (this İs Normally A 6 Month Period But Not Always)

For each month's calculation, use the principal balance obtained after adding the previous month's interest to the bond.

 

5. Re-calculate The Composite İnterest Rate Each Time The İnflation Rate Paid Changes

Then repeat Steps 3 and 4 until the inflation rate changes again or until you reach the current month. When you complete the calculation for the current month, you have found the current value of the bond.

 

Tips and Warnings As a practical matter, the way to calculate I bonds is to use the online calculators provided by Treasury Direct. You may need the serial number of a paper bond to use the calculator.
 

You Might Also Like : How to Calculate a Bond Yield Curve

 

How to Calculate I Bonds Save

Save for later

Found this helpful?

Pin this article to your Pinterest board and come back to it whenever you need a reminder.

Save to Pinterest
Written by

Patrick Harwood

Patrick Harwood has been a professional writer and editor since 2004, specializing in articles about spectator sports, personal finance and law. He has contributed to family of magazines and websites.

More posts
Patrick Harwood

Responses (0)

0%