Backdoor Roth Pro-Rata Calculator

About this calculator

A “backdoor Roth” — contributing after-tax dollars to a traditional IRA and then converting them to a Roth — seems simple, but the IRS's pro-rata rule complicates it if you hold any other traditional, SEP, or SIMPLE IRA balances. The rule requires the taxable portion of every conversion to be calculated across your entire IRA balance, not just the account you're converting: taxable % = pre-tax balance ÷ (pre-tax balance + after-tax basis).

Applying that percentage to your conversion amount tells you the taxable and tax-free portions — this is the calculation reported on IRS Form 8606. Financial planners and DIY investors use this before executing a backdoor Roth to avoid an unpleasant surprise tax bill: even a small pre-tax IRA balance elsewhere can make most of a “backdoor” conversion taxable.