Backdoor Roth Calculator
Estimate pro-rata tax and future tax-free value from a backdoor Roth contribution.
- Last reviewed
- August 26, 2026
- Cost
- Free to use
- Data
- Runs in your browser
- Reviewed by
- Anton Jonson
Tax Owed on Conversion
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Net Amount Converted
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Future Tax-Free Value
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Methodology
How this calculator handles inputs
This calculator uses the values you enter above and applies the formula explained in the guide below. Results update in the browser and are intended for quick planning, comparison, and sanity-checking.
- Use consistent periods, currencies, and units across inputs.
- Review any assumptions before using the result in a decision.
- Recalculate when rates, prices, tax rules, or business terms change.
Important note
This tool provides general planning information only. It is not tax, legal, financial, accounting, or investment advice. Check the current rules for your location and speak with a qualified professional before making a high-stakes decision.
Guide
How it works
Use this calculator to estimate tax owed and future Roth value from a backdoor Roth IRA contribution.
What this calculator does
The backdoor Roth calculator estimates pro-rata tax when existing pre-tax IRA balances are present. It also projects the future tax-free value of the Roth contribution.
It uses:
- contribution amount
- existing pre-tax IRA balance
- current marginal tax rate
- years until retirement and expected return
Backdoor Roth Formula
Taxable % = Pre-Tax IRA Balance ÷ (Pre-Tax Balance + Contribution)
Where:
- Taxable % = pro-rata taxable share
- Contribution = nondeductible IRA contribution
- Tax Owed = contribution × taxable % × tax rate
- Future Value = contribution grown to retirement
Example calculation
If:
- Contribution = 7,500
- Pre-tax IRA balance = 0
- Taxable percentage = 0%
- Tax rate = 24%
Then:
- Tax owed = 0
- Amount converted = 7,500
- Roth assets grow tax-free
- Future value depends on return and time
The clean backdoor Roth conversion tax is 0.
What is a backdoor Roth?
A backdoor Roth is a strategy where someone makes a nondeductible Traditional IRA contribution and converts it to Roth. It is often used when direct Roth IRA contributions are limited by income.
Why backdoor Roth planning matters
- estimates pro-rata tax exposure
- supports high-income Roth planning
- shows future tax-free value
- avoids surprise conversion tax
When to use this calculator
- evaluating a backdoor Roth contribution
- checking pro-rata rule impact
- estimating conversion tax
- projecting Roth value
Common mistakes
- ignoring existing pre-tax IRA balances
- missing pro-rata tax rules
- assuming every conversion is tax-free
- forgetting annual IRA limits
Backdoor Roth vs Roth conversion
Backdoor Roth usually starts with a new nondeductible contribution. Roth conversion moves existing IRA assets into Roth.
The tax treatment can be very different.
FAQs
What is a backdoor Roth?
It is a nondeductible IRA contribution followed by a Roth conversion.
How do you calculate backdoor Roth tax?
Apply the pro-rata taxable percentage to the contribution, then multiply by the tax rate.
What is a good backdoor Roth result?
A good result has low or zero pro-rata tax and fits the annual IRA limit.
What is the difference between backdoor Roth and Roth conversion?
Backdoor Roth uses a new contribution. Roth conversion moves existing assets.
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