Each contract covers one calendar month and settles at 100 minus the average daily effective federal-funds-rate for that month, at $41.67 per basis point on a $5,000,000 notional. Because fomc meetings fall mid-month, a contract's price blends the rate before and after a decision.
Splitting out the meeting-day probability is simple arithmetic and is exactly what the widely quoted "market-implied odds of a cut" are. The calculation weights the pre- and post-meeting days in the month.
Example: a month with an FOMC meeting on day 18 of 30, current rate 4.33%, contract implying an average of 4.21%. The post-meeting rate implied is 4.33 - (0.12 x 30/12) = 4.03%, about 30 basis points below current — a 25-basis-point cut fully priced plus a 20% chance of 50.
Related: federal-funds-rate, fomc, sofr-futures, rate-hike, strip-trade