Backdoor Roth IRA Calculator
See exactly how much of your backdoor Roth IRA conversion is taxable under the IRS pro-rata rule (Form 8606) if you have other pre-tax IRA money — plus your estimated tax bill.
Enter Your Details
Adjust values to see instant results
Taxable Portion of Conversion
Estimated • Based on your inputs
Estimated Tax Owed
$0.00
Detailed Breakdown
Disclaimer: This calculator provides estimates for informational purposes only. Results should not be considered financial, tax, or legal advice. Consult a qualified professional for your specific situation.
How This Calculator Works
Calculation methodology and assumptions
A "backdoor Roth IRA" is a nondeductible contribution to a traditional IRA, immediately converted to a Roth IRA — a workaround for high earners above the direct Roth contribution income limit. The catch is the IRS "pro-rata rule" (IRC Sec. 408(d)(2), calculated on Form 8606 Part II): if you own ANY other traditional, SEP, or SIMPLE IRA money (the IRS "aggregation rule" treats them all as one account), your conversion is taxed proportionally across your ENTIRE traditional IRA balance — you cannot cherry-pick just the after-tax dollars. This calculator applies the Form 8606 formula: tax-free % = (this year's nondeductible basis) ÷ (year-end balance of all other traditional/SEP/SIMPLE IRAs + the amount converted). That percentage of your conversion is tax-free; the rest is taxed as ordinary income at your marginal rate. If you have $0 in other pre-tax IRA money, the conversion is (aside from any growth before converting) essentially tax-free.
How to Use This Investment & Retirement Calculator
- 1
Fill in Nondeductible Traditional IRA Contribution and Investment Growth Before Conversion
Nondeductible Traditional IRA Contribution starts at $7,500; Investment Growth Before Conversion starts at $0. Replace each one with your own figure.
- 2
Fill in Other Pre-Tax Traditional/SEP/SIMPLE IRA Balance and Your Marginal Tax Rate
Other Pre-Tax Traditional/SEP/SIMPLE IRA Balance starts at $0; Your Marginal Tax Rate starts at 24%. Replace each one with your own figure.
- 3
Read the results
The calculator leads with Taxable Portion of Conversion and Estimated Tax Owed, followed by 4 supporting figures.
Example Calculation
What the calculator above returns before you change anything: a $7,500 nondeductible traditional IRA contribution converted to Roth, with $0 in any other traditional, SEP or SIMPLE IRA and a 24% tax rate.
The tax-free share of a conversion is your after-tax basis divided by all of your traditional, SEP and SIMPLE IRA money plus the amount converted (Form 8606). With no other pre-tax IRA money that is $7,500 ÷ $7,500 = 100%.
Result: Taxable amount $0, tax $0. Enter $92,500 of old rollover IRA money instead and only 7.5% of the conversion is tax-free: $6,938 becomes taxable, about $1,665 at 24%.
What Affects Your Results
Rate of Return
Even small differences compound massively over time. 7% vs. 8% over 30 years on $100K means a difference of $200K+. Asset allocation drives your expected return.
Time Horizon
Compounding accelerates exponentially. Most of your wealth is generated in the final years — a 30-year investment earns more in its last 5 years than its first 15.
Contribution Consistency
Regular monthly investments (dollar-cost averaging) smooth out market volatility and ensure you're always buying — including during dips when prices are low.
Fees & Expenses
A 1% annual fee vs. 0.1% fee on a $500K portfolio costs you $4,500/year extra. Over 30 years, high fees can consume 25–30% of potential returns. Use low-cost index funds.
Tips & Best Practices
- Start early. Thanks to compounding, $200/month invested from age 25 to 65 at 8% returns grows to ~$700K. Waiting until 35 cuts that to ~$300K — a $400K penalty for the 10-year delay.
- Don't try to time the market. Research consistently shows that time in the market beats timing the market. Missing the 10 best trading days over 20 years can halve your returns.
- Consider tax-advantaged accounts first: 401(k) (especially with employer match), IRA, HSA. These reduce your tax drag — a 25% tax bracket investor keeps more in a tax-deferred account.
- Rebalance annually. If stocks outperform and grow from 80% to 90% of your portfolio, rebalancing back to 80% locks in gains and manages risk.
- Factor in your state's tax treatment of investment income. Some states exempt certain investment income or have lower rates on capital gains.
StateCalc Team
Editorial Team
The StateCalc team builds financial calculators using data from official government sources including the IRS, U.S. Census Bureau, BLS, and state revenue departments. All formulas are validated by an automated test suite and cross-referenced against published data.
Our editorial standardsFrequently Asked Questions
What is the pro-rata rule for backdoor Roth IRA conversions?
The pro-rata rule (IRC Sec. 408(d)(2)) says that if you have any pre-tax money in ANY traditional, SEP, or SIMPLE IRA, a Roth conversion is taxed proportionally across all of that money combined — not just the specific account or dollars you convert. The IRS "IRA aggregation rule" treats every traditional/SEP/SIMPLE IRA you own as a single account for this calculation, reported on Form 8606 Part II.
How do I avoid the pro-rata rule on a backdoor Roth?
The cleanest way is to have $0 in pre-tax traditional/SEP/SIMPLE IRA money before converting — for example, by rolling any existing pre-tax IRA balance INTO an employer 401(k) plan first (if your plan accepts incoming rollovers), which removes it from the IRA aggregation calculation entirely since 401(k)s aren't included.
What is the 2026 contribution limit for a backdoor Roth IRA?
The nondeductible traditional IRA contribution is limited to the same $7,500 ($8,600 if 50+) annual IRA limit for 2026 — a backdoor Roth doesn't let you contribute more than the standard IRA limit, it just lets high earners get money into a Roth despite the income phase-out.
Does the pro-rata rule include my 401(k) or Roth IRA balance?
No — the pro-rata calculation only counts traditional, SEP, and SIMPLE IRA balances. Money in a 401(k)/403(b)/457 plan (even a rollover IRA that you later roll INTO a 401(k)) or in an existing Roth IRA does not count toward the pro-rata denominator.
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