Backdoor Roth Pro-Rata Calculator
The backdoor Roth is tax-free only when you have no pre-tax IRA balance. If you do, the pro-rata rule taxes a proportional slice of every conversion — often more than people expect. This calculator shows your taxable percentage and the exact tax.
How to use this calculator
- Enter total traditional IRA balance (pre-tax + after-tax).
- Enter after-tax basis (non-deductible contributions).
- Enter amount you plan to convert.
- Enter your marginal tax rate.
- Your results appear instantly below and update as you change the numbers.
How this calculator works
The IRS treats all your traditional IRAs as one pool. Your non-taxable percentage is after-tax basis divided by total balance; every conversion carries that percentage tax-free and the rest is taxable. Example: $20,000 basis in a $100,000 pool makes 20% of a conversion tax-free — a $10,000 conversion has $8,000 of taxable income.
Frequently asked questions
How do I fix the pro-rata problem?
Roll your pre-tax IRA balance into an employer 401(k) before converting — then your traditional IRA holds only basis and conversions are fully tax-free. If you cannot roll it over, converting everything (paying tax once) is usually better than paying tax every year.
Does a 401(k) balance count?
No — only traditional IRAs (including SEP and SIMPLE IRAs) count toward the pro-rata pool. A rollover IRA, however, does count, which is why many people move those into a 401(k) first.
Do I report this on Form 8606?
Yes — non-deductible contributions go on Form 8606 each year, and the taxable part of each conversion is computed there. Skipping the form is the most common backdoor-Roth mistake.
Disclaimer: Results are estimates for general information only and do not constitute financial, tax, or legal advice. Figures reflect 2026 rules and may change. Always confirm current limits and consult a qualified professional before making decisions. Official figures: IRS.gov · 2026 limits per IRS tax inflation adjustments.