The formula for calculating your RMD is to divide your prior year-end account balance by a life expectancy factor found in the IRS Uniform Lifetime Table.
This factor is determined by your age on December 31st of the distribution year.
Step-by-step calculation:
1. Find your prior year-end account balance.
2. Determine your life expectancy factor
3. Divide the balance by the factor
4. Repeat for each account
5. You can combine the totals to take the distribution from any one or more of the accounts.
For additional info:
FYI - you need to determine the RMD for IRA accounts and 401k separately. Your IRA or 401k plan should automatically send you a letter at the beginning of the year saying how much you need to take out. Did she turn 73 in 2025? She can probably log into her IRA account and see how much she needs to take by Dec 31, 2025 or April 1, 2026 for a first year RMD. If she waits until 2026 to take the 2025 RMD then she will have to take 2 RMDs in 2026, one for 2025 and one for 2026.
To determine the RMD you need to use the worksheet on 590-B starting on page 47 and the Life expectancy tables starting on page 50. You use the IRA balance on Dec 31 of the prior year.
https://www.irs.gov/pub/irs-pdf/p590b.pdf