How much of my backdoor Roth conversion is taxable in 2026 or 2027 planning?
Use this backdoor Roth tax calculator to estimate how much of a conversion may be taxable under the IRA pro-rata rule. It compares nondeductible basis with total traditional, SEP, and SIMPLE IRA balances to estimate taxable versus tax-free portions.
backdoor Roth tax calculator
Quick answer
A backdoor Roth conversion is not automatically tax-free. If you have pre-tax IRA money, the pro-rata rule can make part of the conversion taxable based on total IRA balances and nondeductible basis.
Also answers
- backdoor Roth pro rata calculator
- Roth conversion tax calculator
- nondeductible IRA basis calculator
- Form 8606 calculator
Good fit when
- Estimating taxable backdoor Roth conversion amount
- Checking pro-rata rule exposure
- Planning Form 8606 basis tracking
Have ready
- Nondeductible IRA basis
- Total traditional, SEP, and SIMPLE IRA balances
- Conversion amount and tax year
Result you get
Estimated taxable conversion, tax-free conversion, and pro-rata percentage.
How this calculation works
- Adds after-tax contributions and existing basis to calculate total basis.
- Uses the pro-rata formula based on total IRA balances.
- Estimates taxable versus tax-free conversion amounts.
Common mistakes and caveats
- SEP, SIMPLE, and rollover IRAs are included in the pro-rata calculation.
- Year-end IRA balances can change the final taxable portion.
- This estimate does not calculate additional taxes beyond the conversion.
FAQ
Do pre-tax IRA balances affect backdoor Roth taxes?
Yes. The pro-rata rule includes all pre-tax IRA balances when determining the taxable portion.
Last updated & sources
Last updated June 4, 2026.
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