Backdoor Roth Pro-Rata Tax Impact Analyzer

Estimate how the pro-rata rule treats a backdoor Roth conversion before you file Form 8606. Enter your combined pre-tax IRA balance as of December 31, the nondeductible basis carried on Form 8606, the amount you intend to convert, and the marginal tax rate that applies once income is stacked. The analyzer surfaces the taxable portion versus basis recovery, immediate tax due, effective tax rate, and what pre-tax and basis amounts remain so you can decide whether to roll assets into a 401(k), stage conversions, or increase withholding.

Aggregate pre-tax IRA value on December 31 before executing the conversion.
Line 14 of your most recent Form 8606 capturing after-tax contributions waiting to be recovered.
Portion of IRA dollars you intend to convert to Roth this year.
Blended federal and state marginal rate that applies to the taxable conversion amount.

Results assume account values remain stable through December 31 and ignore excise taxes, penalties, or underpayment interest. Coordinate with your tax advisor on rollovers, estimated tax payments, and future Form 8606 filings before executing conversions.

Examples

  • $120,000 pre-tax balance, $10,000 basis, a $6,500 conversion, and a 32% marginal rate ⇒ $6,000.00 taxable, $1,920.00 due, $114,000.00 pre-tax and $9,500.00 basis remaining, for a 29.54% effective rate.
  • $45,000 pre-tax, $5,000 basis, a $15,000 conversion, and a 28% marginal rate ⇒ $13,500.00 taxable, $3,780.00 due, $31,500.00 pre-tax and $3,500.00 basis left, for a 25.20% effective rate.

FAQ

Do I include SEP or SIMPLE IRA balances?

Yes. The IRS aggregates all traditional, SEP, and SIMPLE IRAs when applying the pro-rata rule, so add those balances to the pre-tax input.

How is basis reduced after the conversion?

The tool subtracts the tax-free share of the conversion from your recorded basis, mirroring the Form 8606 calculation.

What if my conversion exceeds total IRA balances?

The analyzer caps the calculation at your combined pre-tax plus basis amount and flags the remainder so you can adjust the planned conversion.

Can I model state taxes separately?

Enter a combined marginal rate that reflects federal, state, and local tax exposure for the most accurate result.

Does the result change if markets move after my conversion?

The pro-rata calculation freezes balances on December 31. If markets rally after a mid-year conversion, the taxable share will still be based on the end-of-year value, so rerun the model with refreshed balances as the year closes.

Additional Information

  • Balances are measured on December 31 to mirror IRS pro-rata calculations on Form 8606.
  • Taxable share equals the conversion multiplied by the ratio of pre-tax dollars to total IRA value after including basis.
  • Rolling pre-tax IRA assets into an employer plan before year-end shrinks the denominator and increases the tax-free portion.
  • Tax due reflects the marginal rate supplied; layer in Medicare surtaxes, NIIT, or withholding adjustments separately.
  • Effective tax rate output helps gauge whether to accelerate basis creation or delay conversions into lower-income years.

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