Treasury Department announces new Series I bond rate of 3.11% for the next six months

I bond rates have a variable and fixed rate portion, which the Treasury adjusts every May and November. Together, these are known as the I bond “composite rate.” You can see the history of both parts of the I bond rate here.

The variable rate is based on inflation and stays the same for six months after your purchase date, regardless of the Treasury’s next announcement. 

Meanwhile, the fixed rate doesn’t change after purchase. This part of the rate is less predictable and the Treasury doesn’t disclose how it calculates the update. 

After the first six months, the variable yield shifts to the next announced rate. For example, if you buy I bonds in September of any given year, your rates change every year on March 1 and Sept. 1, according to the Treasury.  

For example, if you bought I bonds in September 2024, your variable rate would start at 2.96% and change to the new rate of 1.90% in March 2025. But your fixed rate would remain at 1.30%. That would bring your new composite rate to 3.2%.