Backdoor Roth IRA for Business Owners: Step-by-Step Process and the Pro Rata Rule Trap

By Yarik Yarosh, CPA ·September 5, 2026 ·3 min read

Written by Yarik Yarosh, CPA (US & Canada) September 5, 2026 · FL CPA license AC61704 · CPA Ontario

Direct Roth IRA contributions are phased out for high-income taxpayers: the income limit for full contributions is $150,000 (single) / $236,000 (MFJ) for 2025. Business owners whose income exceeds these limits cannot contribute to a Roth IRA directly. The backdoor Roth IRA strategy bypasses this limit through a two-step process that is legal and IRS-acknowledged (the IRS has never challenged it, and the Build Back Better Act’s proposed ban was never enacted).

✓Key takeaway

Backdoor Roth IRA steps:

Contribute to a traditional IRA: $7,000 (2025 limit, $8,000 if age 50+). This is a non-deductible contribution (because the business owner likely has a retirement plan at work or income exceeds the deduction phase-out). Report on Form 8606.
Convert the traditional IRA to Roth IRA: Convert the entire balance to a Roth IRA. If the contribution was non-deductible and there are no earnings yet, the conversion is tax-free. Convert quickly (within days of the contribution) to minimize taxable earnings.

The pro rata rule trap (IRC 408(d)(2)): If the taxpayer has ANY pre-tax traditional IRA balance (from prior deductible contributions or SEP IRA contributions), the conversion is taxed proportionally on ALL traditional IRA balances, not just the non-deductible contribution. This can make the backdoor Roth partially or mostly taxable.

The fix: Roll all pre-tax traditional IRA and SEP IRA balances into a Solo 401(k) or employer 401(k) BEFORE the conversion. 401(k) balances aren’t included in the pro rata calculation. This zeros out the traditional IRA balance, making the backdoor Roth conversion tax-free.

How does the pro rata rule work?

Hypothetical example

Round numbers. A business owner has a SEP IRA with $93,000 (all pre-tax contributions and earnings). They make a $7,000 non-deductible traditional IRA contribution and immediately convert to Roth.

Without understanding the pro rata rule: Expected tax: $0 (converting $7,000 non-deductible contribution)

With the pro rata rule:

Total traditional IRA balances (including SEP): $93,000 + $7,000 = $100,000
Non-deductible (after-tax) portion: $7,000 / $100,000 = 7%
Taxable portion of $7,000 conversion: 93% x $7,000 = $6,510
Tax on conversion (32% bracket): $6,510 x 32% = $2,083

The business owner expected a tax-free conversion but owes $2,083 because the pro rata rule requires proportional taxation across ALL traditional IRA balances.

The fix: Before the conversion, roll the $93,000 SEP IRA into a Solo 401(k). After the rollover:

Total traditional IRA balance: $7,000 (the new non-deductible contribution)
Non-deductible portion: $7,000 / $7,000 = 100%
Taxable portion of conversion: 0%
Tax: $0

The Solo 401(k) must accept the rollover (most do), and the rollover must be completed before December 31 of the conversion year.

Illustrative numbers only, not a real client and not advice for your facts.

Can business owners do a mega backdoor Roth?

Yes, if their Solo 401(k) plan document allows after-tax contributions and in-plan Roth conversions. The mega backdoor Roth allows contributions above the $23,500 employee deferral limit, up to the total annual limit of $70,000 (2025). The difference ($70,000 - $23,500 - employer contribution = the after-tax space) can be contributed as after-tax dollars and immediately converted to Roth within the plan.

This strategy is most commonly used by S-Corp owners with Solo 401(k) plans. The plan must specifically allow after-tax contributions and in-service Roth conversions. Not all plan providers support these features (Fidelity and Schwab do for Solo 401(k) plans).

Want this checked against your own situation?

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Cite this page

Yarik Yarosh, CPA. "Backdoor Roth IRA for Business Owners: Step-by-Step Process and the Pro Rata Rule Trap." Blue Cloud CPA, September 5, 2026. https://bluecloudcpa.com/guides/small-business-backdoor-roth-ira-business-owners

This guide is general information, not tax advice for your specific situation. Which points apply, and how, depends on your facts.