Estimate the tax cost of a backdoor Roth conversion under current IRA contribution limits, including the pro-rata rule impact of existing Traditional, SEP, and SIMPLE IRA balances.
The Backdoor Roth IRA Calculator is for savers who cannot make a full direct Roth IRA contribution and want to estimate the tax cost of contributing to a traditional IRA and then converting to Roth. For 2026, the standard IRA contribution limit is $7,500, with an $1,100 catch-up for age 50 or older. Full direct Roth contributions phase out above modified AGI of $153,000 for single filers and $242,000 for married filing jointly in 2026.
The main complication is the pro-rata rule. If you hold pre-tax money in any Traditional, SEP, or SIMPLE IRA on December 31 of the conversion year, the IRS treats the conversion as coming partly from pre-tax and partly from after-tax dollars. That means even a nondeductible contribution can trigger a taxable conversion.
Enter your intended contribution, existing IRA balances, and marginal tax rate to see how much of the conversion is tax-free, how much is taxable, and how much the pro-rata rule changes the strategy.
A backdoor Roth is straightforward only when your pre-tax IRA balance is zero. This page shows how much tax the pro-rata rule creates when you still hold Traditional, SEP, or SIMPLE IRA money, which helps you decide whether to convert now, wait, or first move pre-tax IRA assets into an employer plan.
Total IRA Balance = Pre-Tax IRA + SEP IRA + SIMPLE IRA + Non-Deductible Contribution After-Tax Ratio = Non-Deductible Basis ÷ Total IRA Balance Taxable Portion = Conversion Amount × (1 − After-Tax Ratio) Tax Cost = Taxable Portion × Marginal Tax Rate
Result: Taxable: $6,522 | Tax: $2,087 | Tax-free: $978
With a $7,500 nondeductible contribution and $50,000 of pre-tax IRA money, the year-end combined IRA balance is $57,500. The after-tax ratio is $7,500 ÷ $57,500 = 13.0%, so only about $978 of a $7,500 conversion is tax-free. The remaining $6,522 is taxable, creating an estimated $2,087 federal tax cost at a 32% marginal rate.
The clean version is simple: no pre-tax Traditional, SEP, or SIMPLE IRA balance at year-end, a nondeductible contribution, then a prompt conversion. Using the 2026 standard limit of $7,500, a fully tax-free conversion growing at 7% for 30 years would reach roughly $57,000.
If you still hold $100,000 of pre-tax IRA money and add a $7,500 nondeductible contribution, only about 7.0% of a $7,500 conversion is tax-free. Roughly $523 would convert tax-free and roughly $6,977 would be taxable. That is why many high earners first roll pre-tax IRA money into a 401(k) or other eligible employer plan if the plan accepts roll-ins.
Some savers use the backdoor Roth every year. Contributing and converting $7,500 annually for 20 years at 7% would build roughly $329,000 of Roth assets, assuming the strategy stays available and pre-tax IRA balances do not trigger pro-rata tax in later years.
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This page treats the entered contribution as after-tax basis and applies the pro-rata rule across the combined year-end balance of Traditional, SEP, and SIMPLE IRAs. The tax-free portion of the conversion equals the conversion amount multiplied by the after-tax basis ratio, and the taxable portion is the remainder. Estimated tax cost is then calculated from the marginal rate you enter.
The worksheet does not model state income tax, prior-year basis already carried on Form 8606, investment gains that occur before conversion, or employer-plan rollovers. It is intended to show how pre-tax IRA balances change the economics of a backdoor Roth strategy under current IRS contribution and reporting rules.
It is a two-step strategy used by some higher-income savers: make a nondeductible contribution to a traditional IRA and then convert that amount to a Roth IRA. The mechanics are simple when there are no pre-tax Traditional, SEP, or SIMPLE IRA balances at year-end.
The IRS treats all of your Traditional, SEP, and SIMPLE IRA balances as one combined pool when you convert. That means the tax-free and taxable pieces of the conversion are determined across the entire pool, not just the account you convert from.
The cleanest workaround is often to move pre-tax IRA money into an employer plan that accepts roll-ins before the end of the conversion year. Employer-plan balances are generally not counted in the IRA pro-rata calculation.
Current IRS rules allow nondeductible traditional IRA contributions and Roth conversions, which is what the backdoor Roth strategy relies on. The tax result still depends on the pro-rata rule, proper Form 8606 reporting, and any future law changes.
Many savers convert soon after making the nondeductible contribution so there is less time for gains to accumulate in the traditional IRA before conversion. Gains that build up before the conversion can create a small additional taxable amount.
Form 8606 is the core reporting form for nondeductible IRA contributions and Roth conversions. Your brokerage will also issue Form 1099-R reporting the conversion distribution.