10/22/2026
Convert $20,000 of after-tax IRA money, and only $769 of it might come out tax free if you also own a large pretax IRA.
It's easy to assume after-tax money converts tax free, since you already paid tax on it once. But the IRS's Form 8606 instructions treat all of your traditional, SEP, and SIMPLE IRAs as one pot, and every conversion takes a proportional slice of that whole pot.
In the hypothetical from our new article, an investor has $20,000 of after-tax contributions and a $500,000 IRA rolled over from an old 401(k). After-tax money is only about 3.8% of their $520,000 total. So $19,231 of the conversion is taxable, which comes to roughly $4,200 of federal tax if it lands in the 22% bracket. Converting from a different IRA doesn't change the math, and once a conversion goes through, it can't be reversed.
The way around it has to do with the calendar. The IRS counts your IRA balances on December 31, and 401(k)s and other employer plans aren't part of the pot. Only pretax money can roll into a plan, so the after-tax dollars stay behind in the IRA. If you have a plan that accepts rollovers and move the pretax money before year end, most of a later conversion could come out tax free. That requires a plan that will take the money, and its fees and fund choices may be worse, so it isn't right for everyone. Married couples figure this separately for each spouse.
We check this before any conversion paperwork goes in. The full article is linked in the first comment.
Hypothetical example for illustration only; not real clients. Assumes no change in balances during the year. Federal tax only; state taxes not included. Educational content, not tax, legal, or investment advice. Talk with your tax professional about your situation.
Full article: https://www.covenantwealthadvisors.com/post/how-to-pay-taxes-on-roth-ira-conversions