Backdoor Roth Pro-Rata Calculator

See how much of your backdoor Roth conversion is taxable when the IRS pro-rata rule applies to your existing traditional IRA balances.

Inputs

Non-deductible IRA contribution (new)

The new non-deductible contribution you made to your traditional IRA that you plan to convert.

Existing pre-tax IRA balance (all IRA accounts)

The total pre-tax (deductible) balance across all your traditional, SEP, and SIMPLE IRA accounts. The IRS aggregates all IRAs for pro-rata purposes.

Existing after-tax (non-deductible) IRA basis

Any prior non-deductible contributions already in your IRAs (your existing Form 8606 basis, not counting the new contribution above).

Amount to convert to Roth

The dollar amount you plan to convert from a traditional IRA to a Roth IRA.

Marginal income tax rate

Your combined federal (and state, if desired) marginal rate. The taxable portion of the conversion will be taxed at this rate.

Results update as you type, and the address bar keeps your numbers so the link you share reopens this exact calculation.

Taxable portion of conversion

$6,140

Detailed results
Tax owed on conversion	$1,474
Tax-free portion of conversion	$860
Effective tax rate on conversion	21.05%
After-tax ratio (basis %)	12.28%

What this result means

Because you have pre-tax IRA funds, the IRS pro-rata rule applies. 87.7% of your total IRA balance is pre-tax, so 87.7% of the $7,000 conversion — $6,140 — is taxable at your 24% rate, resulting in $1,474 in tax owed. Only 12.3% converts tax-free.

Pro-Rata Conversion Breakdown

Step-by-step calculation of how the IRS pro-rata rule splits your conversion.

Pro-Rata Conversion Breakdown. 12 rows, first 12 shown.
Step	Description	Value
1	Existing pre-tax IRA balance	50,000
2	Existing after-tax IRA basis	0
3	New non-deductible contribution	7,000
4	Total IRA balance (all accounts)	57,000
5	Total after-tax basis	7,000
6	After-tax ratio (basis / total)	0.12
7	Pre-tax ratio (1 − after-tax ratio)	0.88
8	Conversion amount	7,000
9	Taxable portion of conversion	6,140.35
10	Tax-free portion of conversion	859.65
11	Tax owed on conversion	1,473.68
12	Effective tax rate on conversion (%)	21.05

How this is calculated

total_ira_balance = existing_pre_tax + existing_after_tax + non_deductible_contribution
total_after_tax_basis = existing_after_tax + non_deductible_contribution
after_tax_ratio = total_after_tax_basis / total_ira_balance
pre_tax_ratio = 1 − after_tax_ratio
taxable_portion = conversion_amount × pre_tax_ratio
tax_free_portion = conversion_amount × after_tax_ratio
tax_owed = taxable_portion × marginal_tax_rate / 100
effective_tax_rate = tax_owed / conversion_amount × 100

The backdoor Roth strategy

A backdoor Roth IRA is a two-step workaround for high earners who cannot contribute directly to a Roth IRA because their income exceeds the IRS phase-out limits. The steps are: (1) make a non-deductible contribution to a traditional IRA — anyone with earned income can do this regardless of income — and (2) convert that traditional IRA balance to a Roth IRA. The result is effectively a Roth contribution made indirectly.

Why the pro-rata rule matters

The IRS does not let you cherry-pick which dollars you convert. Under the pro-rata rule (IRC §408(d)(2)), every conversion is treated as coming proportionally from all of your traditional IRA dollars, both pre-tax and after-tax. If you have $50,000 of old pre-tax money sitting in a rollover IRA and you add $7,000 of new non-deductible money, your total IRA pool is $57,000. Your after-tax ratio is $7,000 ÷ $57,000 ≈ 12.3%. When you convert $7,000, only 12.3% (about $860) converts tax-free; the remaining 87.7% (about $6,140) is taxable ordinary income.

The aggregation rule

A critical and often-overlooked point: the IRS aggregates all of your traditional IRAs for pro-rata purposes, not just the one account you are converting from. This includes rollover IRAs, SEP IRAs, and SIMPLE IRAs (after the two-year holding period). You cannot sidestep the rule by opening a fresh IRA solely for the non-deductible contribution while keeping your rollover IRA at a different custodian. All accounts are pooled.

How to avoid the pro-rata problem

The most effective solution is to eliminate your pre-tax IRA balance before doing the backdoor Roth. The cleanest way to accomplish this is to roll the pre-tax IRA funds into your current employer's 401(k) or 403(b) plan, if the plan accepts incoming rollovers — most do. Defined-contribution employer plans are not included in the pro-rata calculation, so once the pre-tax money moves there your IRA pool contains only the new non-deductible contribution and your after-tax ratio becomes 100%. The conversion is then entirely tax-free.

Form 8606

Any time you make a non-deductible IRA contribution or perform a conversion, you must file IRS Form 8606 with your tax return. This form tracks your cumulative after-tax basis across all years. Failing to file Form 8606 can result in double taxation — you may end up paying tax on money you already paid tax on when you contributed it. Keep copies of every Form 8606 you file because the IRS does not maintain this record on your behalf.

Is the backdoor Roth legal?

Yes. The strategy relies on two separate provisions of the tax code: the ability to make non-deductible contributions (available since 1987) and the ability to convert traditional IRA funds to a Roth IRA (available since 1998 and broadened in 2010). Congress has been aware of the backdoor Roth for years and has declined to close it. A legislative proposal to ban the strategy was included in the Build Back Better Act in 2021 but was not enacted. Until the law changes, the backdoor Roth remains a legitimate planning tool.

Assumptions

All traditional, rollover, SEP, and SIMPLE IRA balances are included in the pro-rata denominator as required by IRC §408(d)(2).
Inherited IRAs are not included in the pro-rata calculation and are excluded from inputs.
The conversion is assumed to occur in the same tax year as the non-deductible contribution.
State income tax is not separately modeled; include it in the marginal tax rate input if desired.
Investment gains between the contribution and conversion dates are not modeled and assumed to be zero or negligible.
Form 8606 must be filed in the year of any non-deductible contribution or conversion.

Frequently asked questions

›What is a backdoor Roth IRA?

A backdoor Roth is a two-step strategy for high earners whose income exceeds the Roth IRA contribution limit. You first make a non-deductible contribution to a traditional IRA, then immediately convert that balance to a Roth IRA. The result is a Roth contribution made indirectly, bypassing the income ceiling that would otherwise prohibit it.

›What is the pro-rata rule and why does it matter for the backdoor Roth?

The pro-rata rule (IRC §408(d)(2)) requires you to treat every IRA conversion as coming proportionally from all of your IRA funds, both pre-tax and after-tax. If you have significant pre-tax IRA money, much of your conversion will be taxable even if you intended to convert only your fresh non-deductible contribution. The rule applies across all your traditional, rollover, SEP, and SIMPLE IRAs combined.

›How can I avoid the pro-rata rule?

The most effective approach is to roll your pre-tax IRA balances into your employer's 401(k) or 403(b) plan before doing the backdoor Roth. Employer plan accounts are excluded from the pro-rata calculation. Once the pre-tax money is in the 401(k), your IRA contains only after-tax basis, and a full conversion is tax-free. Not all employers allow incoming rollovers — check your plan documents first.

›Is the backdoor Roth IRA legal?

Yes. The strategy uses two established provisions of the tax code: non-deductible IRA contributions (available since 1987) and Roth conversions (available broadly since 2010). Congress has been aware of the approach and has not moved to eliminate it. Legislative efforts to restrict it in 2021 failed. It remains a legal and widely-used planning strategy.

›Do spousal IRAs count in the pro-rata calculation?

No. Each spouse's IRAs are calculated separately. The pro-rata rule aggregates all IRAs owned by you individually — it does not include your spouse's IRA accounts. If you are doing a backdoor Roth for yourself, only your own traditional, rollover, SEP, and SIMPLE IRAs are included in your denominator. Your spouse's IRAs are included only in their own pro-rata calculation if they are also doing a backdoor Roth.