Rev. Rul. 2002-62 lists three methods you may use in determining what are substantially equal periodic payments:
- the required minimum distribution method,
- the amortization method, and
- the annuitization method.
All three methods require the use of a life expectancy or mortality table. The second and third methods require you to specify an acceptable interest rate.
Source: https://www.irs.gov/retirement-plans/substantially-equal-periodic-payments