Backdoor Roth IRA Calculator

Frequently Asked Questions

Who needs the backdoor Roth?

High earners above the 2026 Roth IRA income limits: single filers above $165,000 MAGI and married filing jointly above $246,000 MAGI cannot contribute directly. The backdoor strategy works around these limits legally.

How do I avoid the pro-rata tax?

Roll your pre-tax IRA balance into your 401(k) if the plan accepts it. 401(k) balances are excluded from the pro-rata calculation, leaving your IRA entirely non-deductible and the full conversion tax-free.

Is the backdoor Roth legal?

Yes. Congress is aware of the strategy; it is reported on Form 8606, and the IRS has not moved to prohibit it. Tax law could change in the future, so stay informed about any legislative developments.

When is the deadline to contribute?

IRA contributions for a tax year can be made up to the tax filing deadline (usually April 15 of the following year). Converting promptly after contributing minimizes any taxable gains that accumulate before conversion.

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Important Disclaimer: Estimates for informational purposes only.

This calculator provides estimates for informational purposes only. Results are based on assumptions and may not reflect actual outcomes. Consult qualified professionals in relevant fields before making important decisions based on these results.

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How This Calculator Works

The backdoor Roth is a legal workaround that lets high earners who are barred from contributing directly to a Roth IRA still get money into one. You contribute to a non-deductible traditional IRA, then convert it to Roth. This calculator checks whether your income even requires the backdoor, computes your contribution limit ($7,000 base, $8,000 with the age-50 catch-up), and applies the pro-rata rule, which can make part of your conversion taxable if you hold pre-tax IRA money.

It also estimates your mega backdoor capacity if your 401(k) plan supports after-tax contributions, and totals the Roth dollars you can move this year. All figures use 2026 IRS limits.

The Pro-Rata Rule

The pro-rata rule is the key complication in the backdoor Roth. When you convert a non-deductible IRA contribution to Roth, the IRS does not let you cherry-pick only the after-tax dollars. Instead it treats every IRA you own as a single pool and calculates the taxable portion proportionally: taxable % = pre-tax IRA balance ÷ (pre-tax balance + new contribution).

If you have a $63,000 pre-tax IRA and contribute $7,000 non-deductible, your pool is $70,000 with 90% pre-tax. Converting $7,000 means 90% ($6,300) is taxable and only 10% ($700) is tax-free. This trap makes the strategy far less attractive unless your pre-tax IRA balance is zero. The cleanest fix: roll your pre-tax IRA into your current 401(k) plan if it accepts rollovers, removing it from the pro-rata calculation entirely.

Mega Backdoor Roth

The mega backdoor Roth is a separate, much larger strategy available inside some 401(k) plans. The IRS sets a total annual additions limit under section 415(c) - $70,000 for 2026 - that covers your elective deferrals, the employer match or profit-sharing, and after-tax contributions combined. Whatever room remains after your deferral and the employer contribution is your after-tax headroom.

If your plan allows both after-tax contributions and an in-plan Roth conversion (or in-service withdrawal to a Roth IRA), you can move that after-tax money to Roth immediately, triggering little or no extra tax. This can add tens of thousands of Roth dollars per year beyond the standard $23,500 employee limit, but requires specific plan features that not all employers offer.

Form 8606 Requirement

Every year you make a non-deductible IRA contribution or convert IRA money to Roth, you must file IRS Form 8606. This form tracks your cumulative non-deductible (after-tax) basis in traditional IRAs. Without it, the IRS has no record of your basis and may tax you again on the same dollars when you eventually withdraw them - double taxation you can avoid by filing correctly.

Keep copies of all filed Form 8606s indefinitely. The basis tracks across years, decades, and even spousal rollovers. Losing track of the history is one of the most expensive IRA record-keeping mistakes taxpayers make.

Timing and Common Mistakes

Ignoring the pro-rata rule: Any pre-tax traditional, SEP, or SIMPLE IRA balance makes part of every conversion taxable.

Forgetting Form 8606: Without it, you risk being taxed twice on non-deductible contributions.

Letting contributions earn before converting: Gains between contribution and conversion are taxable at ordinary rates; convert promptly.

Assuming every 401(k) supports the mega backdoor: The plan needs both after-tax contributions and in-plan or in-service Roth conversion.

Confusing Roth 401(k) with the after-tax bucket: They are separate features within the same plan.

Tax laws change frequently. Verify current limits at IRS.gov and consult a qualified financial advisor before making retirement decisions.

Backdoor Roth IRA Calculator

Frequently Asked Questions

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