Tool

Backdoor Roth Pro-Rata Check

How much of your Backdoor Roth conversion will be taxable given the pre-tax IRA balances you hold on December 31, and what fixes it.

Non-deductible IRA contribution

2026 limit is $7,500 per person.

Amount you will convert

Traditional / rollover IRAs

SEP-IRA

SIMPLE IRA

Existing after-tax basis

Form 8606 line 14 from last year. Usually zero.

Your marginal tax rate

Federal plus state, on the next dollar of income.

Share of conversion that is taxable

—

Estimated tax on the conversion

—

If you roll pre-tax IRAs into a 401(k)/403(b) first

—

Total after-tax basis (existing + this year)—

All traditional, SEP, and SIMPLE IRA money, plus the conversion—

Taxable amount of the conversion—

Basis carried into next year—

What this assumes

Follows the Form 8606 pro-rata calculation: the non-taxable share equals total basis divided by the year-end value of all traditional, SEP, and SIMPLE IRAs plus amounts converted during the year.
Assumes no investment growth between contribution and conversion. Convert promptly and the difference is pennies.
Roth IRA balances and employer plans (401(k), 403(b), 457(b)) do not count toward the rule.
Each spouse is calculated separately on their own IRAs.

Estimates for education only, not individualized advice. Confirm anything you act on with a professional who knows your full situation.