Our RMD basics guide covers the age-73 start date and the 25% penalty for missing one. What it doesn’t cover is a rule that trips up exactly the people it’s meant to help: which accounts you’re allowed to combine into one withdrawal, and which ones the IRS requires you to treat separately.
IRAs: Calculate Together, Withdraw From Any One
Traditional, SEP, and SIMPLE IRAs can be aggregated. You add up the December 31 prior-year balances of every IRA you own in that category, calculate one combined RMD figure using the Uniform Lifetime Table, and then satisfy that total from any single IRA, split across several, or any combination you choose — the IRS only cares that the total dollar amount comes out, not which specific account it comes from.
401(k)s and Other Employer Plans: No Aggregation, Full Stop
Traditional 401(k)s, 403(b)s (for RMD purposes, though see the note below), and most other employer-sponsored plans cannot be aggregated with each other or with your IRAs. Each plan calculates and pays out its own RMD independently. If you have two old 401(k)s sitting with two different former employers, you owe two separate RMDs — an IRA withdrawal, no matter how large, does not cover either one.
The One Exception on the Employer-Plan Side
403(b) accounts get their own narrow aggregation rule: multiple 403(b)s can be combined with each other, but not with 401(k)s or IRAs. If you’re a nonprofit or educator employee who’s changed jobs and left old 403(b) balances behind, those can share one combined RMD calculation among themselves.
Roth IRAs Don’t Enter the Math
Roth IRAs have no RMD during the original owner’s lifetime, so they’re excluded from the aggregation calculation entirely — don’t count a Roth balance when figuring your combined IRA RMD, and don’t withdraw from a Roth to satisfy a Traditional IRA’s requirement.
The Practical Trap
The most common real-world mistake is treating an old 401(k) like an IRA once RMDs start — assuming a large withdrawal from a Traditional IRA “covers” everything. It doesn’t. If simplifying compliance matters more to you than keeping funds in a former employer’s plan, our 401(k) rollover guide covers the direct-rollover mechanics for consolidating old plan balances into one IRA before RMDs begin — which is exactly what turns multiple separate RMD obligations into one combined calculation.
The Bottom Line
Know which bucket each account falls into before your first RMD year: IRAs aggregate together, 403(b)s aggregate only with other 403(b)s, and 401(k)s stand alone — getting this wrong is the fastest way to trigger the 25% shortfall penalty by accident, not by neglect.
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