How do you calculate the Required Minimum Distribution from an IRA?

By taking the PFMV on 12/31 of previous year for all IRA accounts (Roth doesn't have RMD) and divide your age factor. i.e PFMV = $100,000 and age factor is 22.7 then the RMD would be $4405.29

RMD would be different each year since the PFMV and age factor will change.

Age factor can be find in the 590 Pub on www.irs.gov