Calculators·2026 tax year
Backdoor Roth pro-rata rule calculator
A backdoor Roth is supposed to be tax-free, but if you already have pre-tax money sitting in a traditional IRA, part of your conversion gets taxed anyway. This shows how much.
Taxable part of the conversion
$0
- Tax-free part
- Tax-free share
- Rough federal tax
- Basis left over
How the math works
The IRS treats every traditional, SEP and SIMPLE IRA you own as one big pot. When you convert, you can't pick out only the after-tax dollars. Each dollar you convert is part after-tax and part pre-tax, in the same mix as the whole pot.
So the tax-free share is your after-tax basis divided by the value of all those IRAs on December 31 plus what you converted. That's the math on Form 8606, and it uses the December 31 balance, not the balance on the day you converted. Moving pre-tax IRA money into a 401(k) before the end of the year takes it out of the pot.
Think of it like cream in coffee. Once you pour it in, you can't pour out only the coffee.
Who this is for
For 2026, you can't contribute to a Roth IRA directly once your modified AGI is over $168,000 single or $252,000 married filing jointly, and the amount you can contribute starts shrinking at $153,000 and $242,000. That's why people above those lines use the backdoor.
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An estimate for learning, not tax advice. The tax line uses one bracket, and a big conversion can push you into the next one. I'm a CPA, but I'm not your CPA. Nothing you type leaves your browser. Full disclaimer.