Circle It in Red · Accounts & the Roth machine
You Can't Pour Just the Cream Out: the backdoor Roth and the blender
A note on who Max is. Max is a cartoon owl. He is not a financial advisor, insurance agent, or tax professional, and nothing here is personalized advice. When a question turns personal, he does not answer it — he teaches the general version and points you to a licensed conversation, which is automated and says so before it says anything else.
A man in Naples read about the backdoor Roth, put the year's limit into a nondeductible traditional IRA, converted it the next day, and expected a clean, tax-free move. He also had a large rollover IRA sitting quietly from an old 401(k). The clean move was not clean, and the reason has a name.
The mechanism
The backdoor Roth is two steps. Make a nondeductible contribution to a traditional IRA — after-tax money, basis you have already paid tax on. Then convert that IRA to a Roth IRA. If that were all, the conversion would cost nothing, because you are moving money you already paid tax on.
Here is the part the brochures skip. The pro-rata rule does not look at the one IRA you just funded. At year-end it adds up every traditional, SEP, and SIMPLE IRA you own, measures what share of the whole is after-tax basis versus pretax money, and applies that same share to your conversion. If nearly all of your total IRA money is pretax, then nearly all of what you convert is taxable — no matter which account the dollars physically came from.
That is Pro-Rata Pete, the pelican with a blender for a bill. Once the cream is stirred into the coffee, you cannot pour out just the cream. The rule blends all your IRA money together and makes you convert a spoonful of the mix.
Who it works cleanly for, and who it snags
Clean
- You have no pretax traditional, SEP, or SIMPLE IRA balances at all.
- You can roll any pretax IRA money into a current employer plan before December 31.
Snagged
- You have a large rollover IRA you cannot move into a plan.
- You file Form 8606 wrong, or forget the year-end balance is what counts.
Let me circle the part that bites.
The rollover IRA in the background decides the whole thing.
People do the two visible steps perfectly and never notice the old rollover IRA, because it is not part of the transaction they are looking at. The pro-rata rule does not care what you are looking at. The one move that fixes it: before year-end, roll the pretax IRA money into an employer plan that accepts roll-ins. That empties the traditional-IRA bucket of pretax dollars, so the only thing left to convert is the after-tax contribution you meant to convert. Do it by December 31, because the rule measures the balance on the last day of the year, not the day you convert.
Figures on this page are for tax year 2026 and were last verified 2026-07-25. Tax and benefit numbers change every year — check the current-year figure before acting on any of them. The 2026 Medicare IRMAA income tiers were not yet confirmed when this was written; where they matter, they are named but not stated as fact.
If your question is “does this work for me?”
That depends on balances and a plan document I cannot see. Better question, and one you can answer yourself: do I have any pretax IRA money, and can my employer plan take it in? Two noes and the backdoor is clean. The part that needs your actual accounts is a licensed conversation, not mine.
Traps and topics named in this piece
Max out. Roth well.
Desk’s open.
— Max