RMD Calculator — Methodology

How This Calculator Works

The RMD Calculator projects the required minimum distributions (RMDs) you must take each year from traditional IRAs and 401(k)s, from your RMD start age to age 95. For each year it estimates the extra federal and state income tax the distribution causes, shows whether it pushes you into a higher bracket, and flags years where your income would trigger a Medicare IRMAA surcharge. It also shows how many years you have before RMDs start, which is the usual window for Roth conversions.

Inputs and Assumptions

• Current age: Used to infer your birth year, which sets your RMD start age.
• Traditional IRA and 401(k) balances: As of 31 December of last year.
• Still working: If you are still employed by the 401(k) sponsor, the 401(k) balance is excluded from RMDs (the "still working" exception). IRAs have no such exception.
• Other income: Social Security, pensions and other income, used to place each RMD in your tax brackets.
• Filing status and state: Select the 2026 federal brackets and standard deduction, the state tax rules, and the IRMAA tiers.
• Spouse's age: switched off for now. The joint-life divisors this option used did not match the Joint and Last Survivor Table, so every result uses the Uniform Lifetime Table until they are corrected. If your spouse is your sole beneficiary and more than 10 years younger, your real RMD is lower than shown.
• Expected return: Applied each year to the balance remaining after the RMD.

Formula

birthYear = currentYear − currentAge
startAge  = 73  if birthYear ≤ 1959
            75  if birthYear ≥ 1960

balance grows at r until startAge, then each year:
  RMD      = priorYearEndBalance / divisor(age)
  balance  = (balance − RMD) × (1 + r)

divisor(age) = Uniform Lifetime Table, e.g.
  73: 26.5
  75: 24.6
  80: 20.2
  85: 16.0
  90: 12.2
  95: 8.9

taxOnRMD = [fed(taxable + RMD) − fed(taxable)]
         + [state(taxable + RMD) − state(taxable)]
   where taxable = max(0, otherIncome − standardDeduction)

IRMAA flag when otherIncome + RMD exceeds the first tier
  (2026: $109,000 single / $218,000 married filing jointly)

Data Sources

• Treas. Reg. §1.401(a)(9)-9(c) (as updated by T.D. 9930 for 2022 and later) — the Uniform Lifetime Table, reproduced as Table III in IRS Publication 590-B.
• Treas. Reg. §1.401(a)(9)-9(d) — the Joint and Last Survivor Table, used for a spouse more than 10 years younger.
• SECURE 2.0 Act of 2022, §107, and the final regulations (T.D. 10001, July 2024) — RMD start age 73 for those born 1951–1959 and 75 for those born 1960 or later.
• SECURE 2.0 Act of 2022, §302 (IRC §4974) — the 25% excise tax on a missed RMD, reduced to 10% if corrected in time.
• IRS Revenue Procedure 2025-32 — 2026 federal brackets and standard deductions.
• CMS, "2026 Medicare Parts A & B Premiums and Deductibles" — 2026 Part B IRMAA tiers.
• State revenue departments, tax year 2026 (Tax Foundation's 2026 state rate table as cross-check) — state income-tax brackets, held in our shared state tax data module. States without confirmed 2026 figures use their latest published schedule: California, Idaho, North Dakota, Rhode Island, Vermont and Wisconsin (2025).

Limitations

• Birth year is inferred from your age, so it can be one year early if your birthday has not yet fallen this year. That matters at the 1959/1960 boundary.
• For people born in 1959 the start age is not settled: the final regulations reserve that cohort, and the proposed regulations give 73, which is what we use. It could still become 75.
• Tax is calculated on the RMD only, using the basic standard deduction. It ignores the taxable share of Social Security, the additional deduction for age 65+, the temporary senior deduction, and qualified charitable distributions that can satisfy an RMD.
• IRMAA uses this year's income. Medicare actually looks back two years, so a large RMD affects premiums two years later. Only Part B surcharges are counted, not Part D.
• The "still working" exception does not apply to 5% owners of the employer; this is not checked.
• State tax uses 2026 state brackets (California, Idaho, North Dakota, Rhode Island, Vermont and Wisconsin (2025) on their latest published schedule) applied without state deductions or retirement-income exclusions.
• A single constant return is assumed.

Last Updated

October 2026 — Methodology page published. Uniform Lifetime Table moved to a shared data module and corrected at ages 88 (13.7) and 89 (12.9); the engine had 13.8 and 13.0.