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Backdoor Roth Pro-Rata Tax Calculator
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Estimate how much of your Roth conversion is taxable vs non-taxable when you have both pre-tax and after-tax IRA dollars (Form 8606 “pro-rata rule”).
Inputs
Results
How the pro-rata formula works (IRS Form 8606, simplified)
- Total basis for the year = prior basis + this year’s non-deductible contributions.
- Total year-end IRA value (all Traditional/SEP/SIMPLE) + total distributions in the year = denominator.
- Non-taxable % = total basis ÷ denominator (capped at 100%).
- Non-taxable portion of your conversion = conversion × non-taxable %.
Taxable portion of conversion = conversion − non-taxable portion. - Carryforward basis = total basis − non-taxable portion (not below zero).
Important: The pro-rata rule uses all of your Traditional, SEP, and SIMPLE IRAs combined, and the balance as of Dec 31. Roth IRAs are excluded.
The pro-rata rule is what turns a clean backdoor Roth into a taxable one.
If you hold pre-tax IRA money, the conversion is not the tax-free step it is usually described as. The advisers below pay for the introduction — ask how they would clear the balance first. It is free to you, and it is not the only way to find an adviser.
Before you start, what actually happens. The form is run by Kapitalwise, our advisor-matching partner. Kapitalwise sends your details to advisers who pay for the introduction, so expect calls and texts. Clear Money Guide is paid when you submit the form, whether or not you ever hire anyone. This is free to you and there is no obligation to hire anyone.
The Kapitalwise form opens here — you stay on this page.
What happens when you press the button
It asks about nine questions — age, investable assets, location — then your name, email and phone number, and verifies the phone by text. Nothing loads and nothing reaches Kapitalwise until you press the button.
Next: plan the timing
After you estimate the tax on your conversion, decide how much to convert this year vs later. See: Roth Conversion Windows (fill the bracket, then stop) and QCDs after 70½ (charitable IRA gifts that can reduce AGI).
What to do next
Editorial standards: see our Editorial Policy.
The pro-rata rule is not fixed — the denominator is. The fraction is measured on 31 December, so moving pre-tax IRA balances into an employer 401(k) before then removes them from it entirely, and your after-tax basis is legally barred from following. Order of operations matters, and a SIMPLE IRA inside its first two years blocks it.
The larger version, inside the 401(k): the mega backdoor fills the gap up to $72,000 — the 2026 annual additions limit — using after-tax contributions, with catch-up allowances sitting outside that limit entirely. It depends on two optional plan features, so check those first.