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Your I Bond Purchase
Month and year I bond purchased: 04-01-2025
Amount purchased: $10,000.00
Fixed interest rate: 1.20%
Value of your I bond on 06-01-2025$10,052.00

Source of CPI-U data (inflation): U.S. Bureau of Labor Statistics.

Click on a legend above to hide/show a dataset.

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Monthly Growth of Your I Bond

Month Fixed Rate Inflation Rate Composite Rate[1] Accrued Value[2] Redemption Value
05-01-20251.20%0.95%3.11%$10,024.00 --
06-01-20251.20%0.95%3.11%$10,052.00 --
07-01-20251.20%0.95%3.11%$10,076.00 --
08-01-20251.20%0.95%3.11%$10,104.00$10,024.00
09-01-20251.20%0.95%3.11%$10,128.00$10,052.00
10-01-20251.20%0.95%3.11%$10,156.00$10,076.00
11-01-20251.20%1.43%4.08%$10,192.00$10,104.00
12-01-20251.20%1.43%4.08%$10,224.00$10,128.00
01-01-20261.20%1.43%4.08%$10,260.00$10,156.00
02-01-20261.20%1.43%4.08%$10,292.00$10,192.00
03-01-20261.20%1.43%4.08%$10,328.00$10,224.00
04-01-20261.20%1.43%4.08%$10,364.00$10,260.00

[1] Rate used to calculate the accrued value as of the first of the month, as shown in the first column of the same row.
[2] A bolded amount represents compounded principal on the date in the first column.

Note: You will lose interest for the last three months if you redeem your I bond before holding it for five years. The redemption value in the last column is after taking into account this penalty.

FAQ

You can create a link to a specific I bond in the format below. You can do this by copying the url of the I bond you select. In the first example below, we are linking a $10,000 I bond purchased in November 2020. The value after ibdate is the date of purchase in YYYY-MM format and the value after ibval is the amount without the dollar sign. In the second example we are linking an I bond for $7,534.59 purchased in July 2000.

https://eworkpaper.com/ibond.php?ibdate=2020-11&ibval=10000

https://eworkpaper.com/ibond.php?ibdate=2000-07&ibval=7534.59

You can find the methodology for calculating interest on I bonds on Bogleheads® wiki at the following link:

https://www.bogleheads.org/wiki/I_savings_bonds

The interest rates in a row represent the rates used to compute the bond value in the column "Accrued Value" in the same row. This is the value on the date in the first column in the same row. Redemption Value takes into account the three-month interest penalty for redemption prior to five years.

Composite rate is calculated as follows.

Composite rate = [fixed rate + (2 x semiannual inflation rate) + (fixed rate x semiannual inflation rate)]

The composite rate will never be less than zero. The interest income is computed by applying the composite rate based on the interest computation methodology.

The calculator assumes that you purchased the I bond on the first of the month, and therefore, it uses the CPI-U index for the previous month of purchase as the base CPI-U index.The inflation-adjusted value for a month is calculated as follows.

Inflation-adjusted value = (Purchase value of bond/base CPI-U index) X CPI-U index for the month

Inflation numbers will be updated every month soon after those numbers are released by BLS. Interest rates will be updated soon after they are released every six months by TreasuryDirect. Last update: CPI-U updated on 10/11/2024, I Bond Fixed Rate and Inflation Rate updated on 10/31/2024.

Learn more about I bonds at TreasuryDirect.
Also see the link on Bogleheads® forum: The I Bond Manifesto.
Track Your I Bond in Quicken and Moneydance

Download price history files

Track Your I Bonds in Excel

A spreadsheet solution to track all your I bonds

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