How your RMD is calculated
Once you reach RMD age, the IRS requires you to withdraw a minimum amount from traditional IRAs, 401(k)s, 403(b)s, and similar pre-tax accounts every year; that's how deferred taxes finally get collected. The math is refreshingly simple: take your account balance as of December 31 of last year and divide it by a life-expectancy factor from the IRS Uniform Lifetime Table (the 2022-and-later version, from Publication 590-B, is built into this calculator). The factor shrinks each year, so the required percentage quietly climbs: about 3.8% of your balance at 73, about 8.2% at 90.
The formula
The distribution period is the IRS's estimate of remaining payout years: 26.5 at age 73, 24.6 at 75, 12.2 at 90. One important variant: if your spouse is more than 10 years younger and is your sole beneficiary, you use the Joint Life and Last Survivor Expectancy table instead, which gives a larger factor and a smaller RMD. This calculator uses the standard Uniform Lifetime Table only.
Worked example
$500,000 in a traditional IRA on December 31 last year, turning 75 this year:
RMD = $500,000 ÷ 24.6 = $20,325.20, about $1,693.77/month if you spread it across the year, or roughly 4.07% of the balance. You can always take more; you just can't take less without penalty.
Wasn't the minimum 401(k) withdrawal age 70½?
It was, and if you're searching for "minimum 401k withdrawal at 70 1/2," your information is a couple of law changes out of date. The starting age was 70½ (yes, a half-birthday, a genuinely strange rule) for decades, until the SECURE Act moved it to 72 for anyone reaching 70½ after 2019. SECURE 2.0 then raised it to 73 starting in 2023, and it's scheduled to rise to 75 in 2033. So today, nobody starts RMDs before 73, and if you were born in 1960 or later, you won't start until 75. Two more modern wrinkles: Roth IRAs have never had lifetime RMDs, and starting in 2024, Roth 401(k)s don't either.
The penalty for missing an RMD used to be a brutal 50% of the shortfall. SECURE 2.0 cut it to 25%, and to 10% if you fix the mistake within the correction window (generally two years). Still worth avoiding: your first RMD year lets you delay until April 1 of the following year, but doing so stacks two RMDs into one tax year, which can bump you into a higher bracket.