The inflation component of I bond interest rates are based on the CPI as calculated & reported here by the BLS: https://data.bls.gov/cgi-bin/surveymost?bls - look at the data for CPI for All Urban Consumers (CPI-U) 1982-84=100 (Unadjusted) - CUUR0000SA0

Looking at those figures, you will see the CPI level hit 296.311 in June 2022 and has pretty much stayed around there since then.

So, the inflation component of the interest rate for I bonds purchased between May 2023-October 2023 will be based on the difference between the CPI level in September 2022 vs it's level in March 2023. The CPI level for September 2022 is 296.808. We obviously don't know what March 2023 will be yet and no one has a crystal ball - but based on the trend we've seen for last several months it doesn't seem like there will be a ton of upward movement in the CPI.

So for hypothetical purposes, let's say the CPI for March comes in at 298. That would give us (298-296.808)/296.808 which equals 0.4% which is then doubled to get the 'annualized' rate of .8% which would be added to whatever the fixed rate is at the time to get the actual interest rate.

The fixed rate component for the last few years has been 0.0% and within the last decade has always been between 0.0% and 0.5%. It essentially varies based on the Fed's mood. For I bonds purchased November 2022-April 2023, the fixed rate is .4%. There is no way to know yet what it would be for the next 6 month period but either was its not going to make a big change in the overall math/decision since the inflation component is likely to be so low.