how to calculate series i bonds
the actual rate on the bond known as the composite rate is calculated by combining the fixed and inflation rates the inflation rate impacts the fixed rate set on the bond however the minimum level that the interest rate on a series i bond can fall to is zero which is the floor placed on the bond by the treasury if the inflation rate is so negative that it would take away more than the fixed rate the composite rate will be set at zero the formula for calculating the composite rate is given as composite rate fixed rate 2 x semiannual inflation rate fixed rate x semiannual inflation rate for example if the fixed rate is 0 30 and the semiannual inflation is 2 30 the composite rate on the bond will be however since it is negative in this case the composite ratio will be adjusted to 0 5 27 is the composite interest rate for i bonds issued november 1 2023 to april 30 2024 this includes a fixed rate portion of 1 30 1 inflation adjustments are made 2x each year on may 1 and november 1 