Let's talk about one of the sneakiest RMD rules people trip over every single year Full breakdown: RMD Mistakes & Fixes (taking from the wrong account). — RMD aggregation.
It sounds harmless enough.
"Can't I just total everything up and take one withdrawal?"
Sometimes yes.
Sometimes absolutely not.
And knowing the difference matters, because taking the wrong RMD from the wrong account can trigger penalties, reporting issues, and a headache that ruins someone's entire January.
The problem is that the IRS organizes RMD rules by account type, not by owner.
So the same person can hold two accounts that follow completely different rules for how RMDs must be taken.
Today's blast walks you through the rules in plain English — when you can combine, when you cannot, where mistakes happen, and why people assume all retirement accounts follow the same RMD structure (they don't).
Let's clean it up.
Start with the simplest truth: RMD aggregation is NOT universal.
Most people believe this rule:
"If I have multiple retirement accounts, I can just add up the RMDs and take it all from one account."
That's not how it works.
The IRS only allows aggregation for certain specific account types, and even within those types, there are limits.
So here's the real framework:
There are three categories:
- Accounts you can aggregate
- Accounts you cannot aggregate
- Accounts that sound like they should be aggregated but absolutely cannot
Category 1: IRAs You Can Aggregate
This is the part everyone remembers — because it's the easiest rule.
You can aggregate RMDs from:
- Traditional IRAs
- SEP IRAs
- SIMPLE IRAs
- Rollover IRAs
If you have five Traditional IRAs, you:
- Calculate the RMD for each IRA separately
- Add those RMDs together
- Take the total from any one or combination of your IRAs
This is the one time aggregation makes life easier.
Category 2: Accounts You Cannot Aggregate Under Any Circumstances
This is where people get tripped up.
Employer plans do not follow IRA aggregation rules.
You cannot combine RMDs from:
- 401(k)s
- 403(b)s (special rule below)
- 457(b)s
- TSP
- Employer pension plans
- Each one requires its own RMD
- You can't take the total from one account
- You must satisfy the RMD from each individual plan
It doesn't.
Employer plans stand alone.
Category 3: The 403(b) Exception — Yes, They Can Aggregate (But Only With Each Other)
This one is fun because it's not intuitive at all.
403(b) plans can aggregate RMDs — but only with other 403(b) plans.
Not with:
- 401(k)s
- IRAs
- 457 plans
- They calculate each RMD separately
- Add them together
- Take the total from any one 403(b)
This is a rule left over from decades ago when 403(b)s were governed under different regulations, and Congress kept the exception alive.
Most people think they imagined this rule when they first hear it.
It's real.
Inherited accounts follow their own rules — and they often surprise people.
Inherited accounts bring another twist.
Inherited IRAs
You can aggregate RMDs across inherited IRAs only if:
- They came from the same original decedent
- They are the same type (both Traditional or both Roth)
- They follow the same distribution rule (stretch vs 10-year rule)
Inherited accounts follow the source, not the owner.
Inherited employer plans
No aggregation.
None.
Ever.
If someone inherits two 401(k)s from two different employers, each plan demands its own RMD.
Roth accounts are the easiest category — but only during your lifetime.
Here's the clean version:
- Roth IRAs: No lifetime RMDs.
- Roth 401(k)/403(b): RMDs required unless rolled into a Roth IRA (rules change in 2024 under SECURE 2.0, but operational errors still happen).
- Inherited Roth IRAs: RMDs do exist, but you still cannot aggregate them with employer plans or Traditional accounts.
Why does the IRS separate all of this?
Because each account type is governed under a different section of the tax code:
- IRAs → IRC Section 408
- 401(k)s → Section 401
- 403(b)s → Section 403
- 457(b)s → Section 457
- Pensions → Section 414
- Inherited accounts → follow the decedent, not the recipient
The aggregation rules are just leftovers from how each category developed.
To the IRS, they're clean and logical.
To everyone else, they feel completely random.
Where mistakes usually happen
You'll see these errors every single RMD season:
Mistake #1: Taking one big RMD from a 401(k) and thinking it covers everything.
It doesn't.
Mistake #2: Rolling employer plans into an IRA mid-year without taking the plan RMD first.
RMDs must be taken before the rollover.
Mistake #3: Aggregating inherited IRAs that came from different people.
The IRS doesn't allow cross-decedent mixing.
Mistake #4: Assuming Roth accounts never require RMDs.
Inherited Roth IRAs absolutely do.
Mistake #5: Thinking "IRA rules" apply universally across all retirement accounts.
Employer plans operate on a different planet.
Let's summarize this in one clean sentence.
You can aggregate RMDs for IRAs with IRAs, and 403(b)s with 403(b)s — everything else must stand alone.
That's the entire rule.
If people understood that one sentence, January would be a lot quieter.
I write one of these every day, one retirement rule, explained in plain language and verified against the source. The daily email is free: subscribe here.
Disclaimer
This Knowledge Blast is for educational and informational purposes only. It is not tax, legal, or financial advice, and it does not create an advisor–client relationship. Always consult appropriate professionals for decisions about your own situation.