A backdoor Roth IRA is two ordinary steps: a nondeductible contribution to a traditional IRA, then a conversion of that money to a Roth IRA. It gets money into a Roth when your income is too high to contribute directly. The tax result depends on one rule, the pro-rata rule, which the calculator below works out from your numbers.
Who uses a backdoor Roth
People whose income is above the Roth IRA limits. For 2026, direct Roth contributions phase out between $153,000 to $168,000 of modified AGI for single filers and $242,000 to $252,000 for married couples filing jointly. Above the top of the range you cannot contribute directly at all. There is no income limit on contributing to a traditional IRA or on converting to Roth, which is what the backdoor relies on.
How to do a backdoor Roth IRA, step by step
- Contribute to a traditional IRA without deducting it: up to $7,500 for 2026, or $8,600 at 50 and over, until April 15, 2027.
- Convert it to your Roth IRA. Most providers do this online. Any growth between the contribution and the conversion is taxable.
- File Form 8606 with your tax return. It records the nondeductible contribution as basis and works out how much of the conversion is taxed.
The pro-rata rule
The IRS treats all your traditional, SEP and SIMPLE IRAs as one account when you convert. You cannot convert only the after-tax dollars. The tax-free share of any conversion is your total basis divided by the value of all those IRAs on December 31 plus the amount converted:
Tax-free share = basis ÷ (December 31 balance of all traditional, SEP and SIMPLE IRAs + amount converted)
An example. You contribute $7,500 nondeductible and convert it, but you also hold $42,500 of pre-tax money in a rollover IRA on December 31. Your basis is $7,500 out of $50,000, so 15% of the conversion is tax-free: $1,125. The other $6,375 is taxed as income, and $6,375 of basis carries forward to future years.
Pro-rata calculator
15% of the conversion is tax-free. Of the $7,500 you convert, $6,375 is added to your taxable income, because the other IRA money you hold on December 31 is mostly pre-tax.
Keeping the conversion tax-free
- Roll pre-tax IRA money into a workplace plan before December 31 of the conversion year, if your 401(k) or 403(b) accepts roll-ins. Balances in a 401(k) or 403(b) do not count in the pro-rata calculation.
- Your spouse’s IRAs do not count. The rule applies to each person separately, so each spouse runs their own backdoor Roth and files their own Form 8606.
- Convert soon after contributing so there is little growth to tax, and keep the traditional IRA at zero afterwards.
Form 8606, line by line
- Line 1: your nondeductible contribution for the year.
- Line 2: basis left from earlier years (last year’s line 14). Line 3 adds them.
- Line 6: the value of all your traditional, SEP and SIMPLE IRAs on December 31, after the conversion.
- Line 8: the amount converted. Line 9 adds lines 6, 7 and 8.
- Line 10: line 5 divided by line 9, at most 1. This is the tax-free share.
- Line 11: the tax-free part of the conversion. Line 14 is the basis you carry forward.
- Lines 16 to 18: the conversion, its tax-free part and the taxable part that goes on your Form 1040.
You file Form 8606 for every year you make a nondeductible contribution or convert, even if nothing is taxed.
Timing
The tax law sets no waiting period between the contribution and the conversion. A contribution for 2026 can be made until April 15, 2027, but the conversion is reported in the calendar year it happens, and the December 31 balance used for the pro-rata rule is the one at the end of that year.
The mega backdoor Roth
Some 401(k) plans allow after-tax contributions beyond the $24,500 employee limit, up to the $72,000 total for 2026 including employer money, and allow converting them to Roth inside the plan or rolling them to a Roth IRA. That is called a mega backdoor Roth. It depends entirely on your plan’s rules.
Is the backdoor Roth still allowed?
Yes. In 2021 the House passed a bill that would have ended backdoor and mega backdoor Roth conversions, but the provision was dropped in the Senate and never became law. No ban has been enacted since; we last checked on October 17, 2026. Larger pre-tax balances are covered by the Roth conversion calculator, and direct contributions by the Roth IRA calculator.
Figures checked on against IRS, About Form 8606, Nondeductible IRAs, IRS Publication 590-A, Contributions to Individual Retirement Arrangements and IRS, 401(k) limit increases to $24,500 for 2026, IRA limit increases to $7,500 (IR-2025-111, Notice 2025-67).