For retirees who consolidated a career into three or four different retirement accounts — an old 401(k) from a decade-ago employer, a current employer's plan, a rollover IRA, and maybe a 403(b) from a stint in the nonprofit world — the required minimum distribution rules are not one rule. They are three, and mixing them up carries a 25% excise tax on whatever amount was supposed to come out and did not.
The core question every retiree with multiple accounts faces at age 73: can I take one combined withdrawal to satisfy every RMD, or do I have to slice each account separately? The answer depends entirely on what kind of account holds the money.
IRAs Get the Pool Treatment
Traditional IRAs, SEP IRAs, and SIMPLE IRAs all share a single set of aggregation rules. The IRS requires the account holder to calculate the RMD for each IRA separately — dividing the December 31 prior-year balance by the applicable life expectancy factor — and then permits the total to be pulled from any one IRA, any combination, or all of them proportionally. The choice is entirely the retiree's.
The practical value is significant. A retiree with three IRAs holding cash, laddered Treasurys, and a precious metals allocation inside a self-directed account can take the entire aggregate RMD from the cash IRA rather than being forced to sell bullion or unwind a bond ladder at an inconvenient moment.
403(b) Plans Have Their Own Pool
Multiple 403(b) accounts, common among teachers, hospital workers, and university employees, follow the same logic as IRAs — but only among themselves. Two 403(b) balances can be combined for RMD purposes, but a 403(b) cannot be aggregated with an IRA. Each family of plan sits in its own bucket.
401(k) Plans Do Not Aggregate
This is the rule that catches retirees off guard. Every 401(k) plan that owes an RMD must have that RMD taken from that specific plan. A retiree with two old 401(k)s that generate RMDs of $5,000 and $3,000 cannot take $8,000 from one and satisfy both. The IRS treats the second plan as having missed its distribution entirely and applies the excise tax to the shortfall.
Cross-plan aggregation is also prohibited across account types. A 401(k) RMD cannot be pulled from an IRA. A 403(b) RMD cannot be pulled from a 401(k). And an inherited IRA RMD — a category that includes many post-SECURE Act beneficiaries now subject to annual withdrawals inside the 10-year window — sits in its own separate silo. It cannot be combined with the beneficiary's own IRA RMDs.
The Penalty for Getting It Wrong
SECURE 2.0 reduced the RMD excise tax from 50% to 25%. If the shortfall is corrected within two years and the retiree files Form 5329 with a reasonable-cause explanation, the penalty drops further to 10%. But those are consolation figures — the intended tax outcome is still a fully satisfied RMD with no penalty at all.
Two Practical Defenses
Consolidate old 401(k)s into an IRA before age 73. Rolling a former employer's 401(k) balance into a traditional IRA turns a per-plan obligation into a single aggregated calculation and eliminates the risk of overlooking a small legacy account. The still-working exception may let the current employer's plan defer RMDs, but old plans do not qualify.
Keep an inventory of every account that owes an RMD. A single spreadsheet listing account type, custodian, December 31 balance, calculated RMD, and the actual withdrawal source is the cheapest insurance available against a 25% penalty. Custodians will report distributions, but they will not tell the retiree whether the wrong account was tapped.
The aggregation rule is one of the few places in retirement tax law where a simple administrative move — a rollover, or a checklist — meaningfully lowers the odds of an expensive filing mistake.
Sources: Internal Revenue Service, Charles Schwab, Fidelity, Kiplinger, Wealthvieu, Life Money USA