The fixed rate of return is determined when the bond is purchased. The variable rate is calculated semiannually based on the inflation rate.
The variable rate on an I Savings Bond is determined using the Consumer Price Index for Urban Consumers (CPI-U) for the months of May and November of each year. Fixed rates and semiannual inflation rates are combined to determine composite earnings rates. An I Bond’s composite earnings rate changes every six months after its issue date.
Fixed and variable rates for I Savings Bonds issued over the last 10 years are posted on the Treasury Direct Web site (www.treasurydirect.gov).
What if the value of the CPI is falling?