Backdoor Roth Pro-Rata Rule Calculator
If you have any pre-tax money in any Traditional IRA, the IRS pro-rata rule taxes most of your backdoor Roth conversion. Calculate exactly how much.
| Total IRA balance (pre-tax + basis) | — |
| Conversion amount | — |
| Taxable percentage (pre-tax / total) | — |
| Taxable portion of conversion | — |
| Non-taxable basis portion | — |
| Federal tax owed | — |
The IRS pro-rata rule turns a tax-free backdoor Roth conversion into a tax bill when you have any pre-tax money in any Traditional, SEP, or SIMPLE IRA. This calculator shows your exact taxable conversion amount, so you don't get a surprise on Form 8606 at tax time.
How the Pro-Rata Rule Works
When you convert any Traditional IRA money to Roth, the IRS treats the conversion as proportional to your total IRA balance. If 95% of your IRA balance is pre-tax and 5% is after-tax basis, then 95% of your conversion is taxable — regardless of which specific dollars you converted. The formula uses your December 31 IRA balance across ALL Traditional, SEP, and SIMPLE IRAs you own (but not your spouse's, and not Roth or 401(k) accounts).
How to Avoid Pro-Rata
The cleanest workaround: roll pre-tax IRA money INTO your employer 401(k) before converting. Once the IRA balance is $0, your $7,000 after-tax contribution converts 100% tax-free. Not all 401(k) plans accept reverse rollovers — check with HR. Other options: (1) convert all pre-tax IRA money over multiple years (slow but works), (2) qualify the entire IRA for Roth conversion now if your tax bracket is unusually low (e.g., retirement gap year).
Form 8606 — File Every Year
Track your IRA basis on Form 8606 for every year you make non-deductible contributions or conversions. Losing track of basis can mean paying tax twice on the same dollars. The IRS does NOT track basis for you. Keep copies of every 8606 indefinitely. See our 457(b) vs 403(b) vs 401(k) calculator for the public-sector retirement comparison.
Last updated May 2026. Sources: IRS Rollovers After-Tax.