Savings Bond Calculator

Frequently asked questions

Why build another I bond calculator when TreasuryDirect already has one?

TreasuryDirect's own Savings Bond Calculator is an accurate source for paper bonds, but this program requires users to input serial numbers individually along with denominations of individual bonds on a dated interface, which causes some users to find the process slow when trying to check multiple bonds. This tool eliminates the need for a serial number, since none is needed to get a value estimate, only the issue date and how much was purchased. With the ability to view all bonds in one table, users have access to their entire I bond holdings rather than having to check each bond separately.

Where does the rate data come from?

TreasuryDirect's own published I Bond Rate History, the same fixed-rate and semiannual inflation-rate figures the Treasury itself announces every May 1 and November 1, sourced directly from their published spreadsheet rather than recomputed or estimated by this site.

Why do I need the issue month instead of just the purchase date?

Because the date you purchased your I bond determines the two pieces of your I bond's total rate. The fixed rate earned by all I bonds is determined when an I bond is issued (the purchase date) and stays the same for as long as you hold that I bond. The inflation-adjustment portion of your I bond adjusts every six months from the anniversary of the date it was issued. A person buying an I bond in late April and a person buying an I bond in early May could earn a significantly higher or lower fixed rate than each other, because they fall in a different 6-month period of issuance.

What is the composite rate and how is it calculated?

The total interest rate of a bond during a 6-month time frame is calculated as follows: (1) the fixed rate of the bond, (2) twice the inflation rate that has been reported by the Treasury over the past 6 months, and (3) the product of the fixed rate of the bond and the inflation rate reported over the last six months. This formula is published by the Treasury and applies to all bonds issued. The fixed rate stays constant throughout the duration of the bond. However, the inflation rate changes with each new 6-month reporting cycle, so the overall interest rate of a bond may increase or decrease at least once per 6 months depending on changes in inflation rates and not on changes to the bond itself.

Why does the tool show two different values?

The accrued value is what your bond has really earned. The redeemable value is how much money you would get back if you sold the bond today. This is important to know because when you hold an I bond for less than 5 years, you give up the last three months' worth of interest as a penalty for selling too soon. You cannot sell or redeem any I bond that is less than 1 year old, by law, so no redeemable amount is shown for those.

Is this exact to the penny?

It is based upon the Treasury's official, publicly available interest rate and methodology of compound interest (the six-month interest accrued monthly and compounded every six months), so this tool should provide an accurate representation of what you can expect to receive in redemptions. However, it does not link to TreasuryDirect to obtain information about your specific bonds, so treat this as a tool for planning, and go directly to TreasuryDirect or the official Treasury website to get an exact figure for a real transaction.

Is my bond information private?

Yes. Every bond you add is stored in this browser's own IndexedDB, on your device, and never sent anywhere, not even a serial number is asked for. There's no account and no bank or TreasuryDirect login, so clearing your browser data or switching devices starts you over.