What is an I bond composite rate?
A Series I savings bond’s composite, or combined, rate uses a fixed rate and a semiannual inflation rate. TreasuryDirect publishes the formula: fixed rate + twice the semiannual inflation rate + the product of the two rates. The fixed rate stays with a bond for its life, while the inflation component changes every six months. This calculator uses the formula and dated inputs you supply; it does not load or assume a current rate.
How does the six-month rate reset work?
Treasury announces rate components in May and November, but a particular bond’s rate changes every six months from its issue month. For example, a bond issued in November resets in May and November. Interest accrues monthly and is added to principal every six months. This page shows the reset months and estimates one six-month period from a single rate scenario; future inflation rates are unknown and must be entered separately when available.
The calculator rounds the annual composite rate to the nearest 0.01 percentage point and floors a negative result at zero, consistent with TreasuryDirect’s published method. It then applies half of that annualized rate to the entered starting principal for a transparent scenario. This simplified arithmetic is useful for understanding the rate formula, but it does not reproduce all monthly accrual and value-display conventions or the official value of a particular bond.
When can an I bond be redeemed?
TreasuryDirect says an I bond cannot be redeemed during its first 12 months. If redeemed before it is five years old, the last three months of interest are forfeited. Bonds otherwise earn interest until redemption or 30 years, whichever comes first. These restrictions are not included in the scenario result, so the displayed ending balance must not be treated as cash available at an assumed date.
For an electronic bond, check its value in your TreasuryDirect account. TreasuryDirect’s Savings Bond Calculator is for paper bonds and can show values through the remaining months in the current six-month interest period. Verify issue date, denomination, rate history, and redemption eligibility with TreasuryDirect before relying on a bond value. Rates and rules on this page were checked 2026-11-03; the rate inputs remain your responsibility.
This educational tool is not a recommendation to buy or redeem a savings bond and is not financial, tax, or legal advice.
Frequently asked questions
Does the fixed rate change when inflation resets?
No. TreasuryDirect says a particular I bond’s fixed rate stays the same for its life; the inflation rate and resulting composite rate change every six months.
Does this calculate the exact value in my account?
No. It estimates one six-month scenario from user inputs. Use TreasuryDirect’s account value for an electronic bond or its Savings Bond Calculator for a paper bond.
Can I cash an I bond at any time?
No. TreasuryDirect says you must hold it at least 12 months. Cashing before five years results in losing the last three months of interest.
Where do I get the rates to enter?
Use TreasuryDirect’s I bonds interest-rates page and record the date you checked. Make sure the fixed rate applies to the bond and the inflation rate applies to the six-month period you are modeling.