Your RMD for a particular year is the previous year's year-end balance divided by the life-expectancy factor for the particular year. Your life-expectancy factor for the particular year is the factor from the Single Life Expectancy Table (https://www.irs.gov/publications/p590b#en_US_2021_publink100089977) for your age attained in 2021 reduced by 1 for each subsequent year. For example, if you attained age 64 in 2021, the factor for 2022 would be 23.7 - 1 = 22.7.
