Backdoor Roth IRA Pro-Rata Calculator 2026

Not tax or legal advice. 2026 Roth IRA contribution limits per IRS Notice 2025-67. The pro-rata rule applies under IRC §72(e). Consult a qualified tax advisor before executing any IRA contribution or conversion.

If your income exceeds $252,000 (married filing jointly) or $168,000 (single) in 2026, you cannot contribute directly to a Roth IRA. The backdoor Roth — a non-deductible Traditional IRA contribution followed immediately by a Roth conversion — is the standard workaround. But it contains a trap most high-income executives walk into: the pro-rata rule.

If you have pre-existing pre-tax Traditional IRA balances (rollover IRAs from past employers are the most common source), the IRS requires you to treat all your IRAs as one pool when calculating what fraction of any conversion is taxable. You cannot cherry-pick just the non-deductible dollars. The result: a "backdoor Roth" on a $7,500 contribution costs thousands in unexpected ordinary income tax.

This calculator shows you exactly how much the pro-rata rule costs you — and whether rolling your pre-tax IRA into your employer's 401(k) plan would eliminate it entirely.

Pro-Rata Rule Calculator

Understanding the Pro-Rata Rule

The backdoor Roth IRA works perfectly when you have no pre-tax money in any Traditional, SEP, or SIMPLE IRA. In that case, your $7,500 non-deductible contribution converts to Roth with zero additional income tax. But the IRS aggregates all your IRAs for the pro-rata calculation — your 2022 rollover IRA from your last employer doesn't stay siloed.

The IRS formula (Form 8606, Part II) is:

Non-taxable conversion fraction = Total non-deductible basis ÷ (Year-end IRA balance + Total conversions this year)

Example: You have a $500,000 rollover IRA from a prior employer (all pre-tax). You contribute $7,500 non-deductible and immediately convert it to Roth.

• Denominator: $500,000 (year-end IRA) + $7,500 (conversion) = $507,500
• Non-taxable fraction: $7,500 / $507,500 = 1.48%
• Taxable: $7,500 × 98.52% = $7,389
• At 37% federal: you owe $2,734 to move $7,500 into a Roth

That's a very poor trade. The backdoor Roth works only if you clear the pre-tax IRA balance first.

Which IRA accounts are aggregated?

All traditional IRAs you own are aggregated — including rollover IRAs, SEP-IRAs, and SIMPLE IRAs (after the 2-year holding period). IRAs belonging to your spouse are not aggregated with yours — each spouse calculates separately. 401(k), 403(b), and 457 plan balances are not aggregated, which is why rolling a traditional IRA into a 401(k) clears the pro-rata trap.

Strategy: Roll Pre-Tax IRA to Employer 401(k)

If your employer's 401(k) plan accepts incoming rollovers from traditional IRAs (most do), you can move the entire pre-tax IRA balance into the 401(k) before year-end. Once the rollover is complete and your year-end traditional IRA balance is zero, your $7,500 non-deductible contribution converts to Roth 100% tax-free.

What to check with your plan administrator:

• Does the plan accept traditional IRA rollovers? (Most plans do; some don't.)
• Is the rollover pre-tax money only — or are there after-tax IRA amounts that need to stay outside?
• When is the rollover effective for IRS purposes? (It must be completed before December 31 of the year you plan the backdoor Roth.)

Note: Self-employed individuals with SEP-IRAs can roll the balance into a solo 401(k) (if they set one up with incoming rollover authority) to achieve the same result. This is a common strategy for highly-compensated partners and consultants who would otherwise be stuck with a large SEP balance blocking their backdoor Roth.

Mega Backdoor Roth: The $47,500+ Opportunity

If your employer 401(k) plan allows after-tax (non-Roth) contributions AND in-service distributions or conversions, you have access to a much larger Roth contribution channel known as the mega backdoor Roth.

The IRS §415(c) limit on total 401(k) annual additions in 2026 is $72,000 (not counting catch-up). This cap covers:

• Your pre-tax or Roth salary deferrals: up to $24,500
• Employer matching and non-elective contributions: e.g., $8,000–$12,000
• After-tax contributions (your additional voluntary contributions): the remaining space

The mega backdoor Roth is entirely separate from the regular backdoor Roth and has no pro-rata rule issue — after-tax 401(k) contributions have full basis immediately, and in-plan Roth conversions convert them at a 0% taxable fraction. The only constraint is whether your plan allows it.

2026 Roth IRA Contribution Limits and Income Phaseout

2026 contribution limit: $7,500 (under age 50); $8,600 (age 50+ with $1,100 indexed catch-up). Source: IRS Notice 2025-67. At UHNW income levels, the phaseout is irrelevant — full ineligibility applies.

When the Backdoor Roth Doesn't Make Sense

1. Large unconvertible pre-tax IRA with no 401(k) to receive rollovers. If you're retired, self-employed with no employer plan, or your plan doesn't accept incoming rollovers, you may be stuck paying the pro-rata tax every year. Run the calculator above — if the tax cost approaches or exceeds the expected benefit of tax-free growth, the regular backdoor Roth may not be worth executing. A UHNW-focused Roth conversion strategy (converting large IRA balances in lower-income years) may be more efficient.

2. California residents. California does not recognize non-deductible IRA contributions — there is no California equivalent of Form 8606. That means California treats your backdoor Roth conversion as if it were 100% taxable, even if the federal calculation shows a non-taxable fraction. At CA's 13.3% rate, this adds meaningful cost for residents with large pre-tax IRA balances.

3. Short investment horizon in the Roth. Roth conversions and backdoor Roths pay off through long-term tax-free compounding. If the funds will be distributed within a few years, the break-even calculus shifts against conversion. The Roth conversion break-even calculator models this precisely.

4. Already past the 2-year SIMPLE IRA restriction. SIMPLE IRA balances can't be rolled to a 401(k) or traditional IRA during the first 2 years of participation. If you're within that window, you can't clear the SIMPLE from the pro-rata calculation yet.

Related Calculators and Guides

• Roth Conversion Break-Even Calculator — for large conversions, IRMAA cliff detection, and estate tax benefit quantification
• Roth Conversion Strategy for UHNW Families — when to convert, bracket-filling windows, inherited Roth IRA advantages
• RMD Calculator 2026 — model the forced distribution schedule that makes pre-conversion valuable
• IRMAA Calculator 2026 — Roth conversions affect Medicare premiums; model the cliff crossings before executing
• UHNW Retirement Income Planning — how Roth accounts fit into a multi-decade withdrawal sequence
• Executive Compensation Planning — NQSOs, ISOs, RSUs, and NQDC for high-income executives navigating multiple tax strategies simultaneously