How to Use This Calculator
- 1
Enter Your IRA Details
Input your Traditional IRA contribution amount, conversion amount, existing Traditional and Roth IRA balances, marginal tax rate, investment horizon, and expected annual return.
- 2
Review Your Results
The calculator displays three result cards — Estimated Tax Liability, Tax-Free Future Value, and Tax Savings vs Traditional — plus an insights card showing the pro-rata breakdown, Roth balance after conversion, effective conversion cost, and traditional after-tax comparison.
Example Calculation
A high-income earner with $50,000 in a pre-tax Traditional IRA contributes $7,000 and immediately converts to a Roth IRA, at a 25% tax rate, projecting 20-year growth at 7%.
Traditional IRA Contribution ($)
7,000
Roth IRA Conversion Amount ($)
7,000
Traditional IRA Balance Before Conversion ($)
50,000
Roth IRA Balance Before Conversion ($)
10,000
Income Tax Rate (%)
25
Years to Grow
20
Expected Annual Return (%)
7
Results
Estimated Tax Liability
$1,535
Tax-Free Future Value
$65,785
Tax Savings vs Traditional
-$79,329
Insights card shows Roth balance after conversion ($17,000), taxable conversion under pro-rata rule ($6,140 at 87.
Tips
Roll Pre-Tax Funds to a 401(k) First
With a $50,000 pre-tax Traditional IRA, 87.7% of your $7,000 conversion is taxable, costing $1,535 in taxes. If you roll those pre-tax funds into a 401(k) first so your Traditional IRA balance is $0, the pro-rata taxable amount drops to $0 and your tax liability becomes $0 — saving the full $1,535.
Lower Pre-Tax Balances Slash Conversion Costs
Reducing your pre-tax Traditional IRA from $50,000 to $5,000 before contributing and converting $7,000 drops the pro-rata ratio from 87.7% to 41.7%. Your tax liability falls from $1,535 to $729, and the effective conversion cost drops from 21.9% to 10.4%.
Longer Horizons Amplify Roth Growth
Extending your time horizon from 20 to 30 years increases the Roth future value from $65,785 to $129,408 — nearly doubling your tax-free balance. However, with a large $50,000 pre-tax Traditional IRA, the tax savings vs traditional widens to -$156,051, reinforcing the need to clear pre-tax balances first.
Tax Rate Matters for Conversion Cost
At a 22% tax rate instead of 25%, the tax liability on the same $7,000 conversion with a $50,000 pre-tax balance drops from $1,535 to $1,351, and the effective conversion cost falls from 21.9% to 19.3%. Model different rates to find your optimal conversion year.
The Logic Behind Backdoor Roth IRA Conversions
The core calculation determines how much of your conversion is taxable using the IRS pro-rata rule, then projects long-term Roth growth versus keeping funds in a Traditional IRA.
totalTradBalance = tradBalanceBefore + contribution
proRataRatio = tradBalanceBefore / totalTradBalance
taxableConversion = conversionAmount x proRataRatio
taxLiability = taxableConversion x (incomeTaxRate / 100)
rothBalanceAfter = rothBalanceBefore + conversionAmount
rothFutureValue = rothBalanceAfter x (1 + annualReturn)^years
tradFutureValue = tradBalanceBefore x (1 + annualReturn)^years
tradAfterTax = tradFutureValue x (1 - incomeTaxRate / 100)
taxFreeGain = rothFutureValue - tradAfterTax
effectiveCostRate = taxLiability / conversionAmount
The pro-rata rule treats all your IRA assets proportionally — even though you are converting newly added after-tax dollars, a large pre-tax balance drives most of the conversion into taxable territory.
The taxFreeGain compares the projected Roth value against what the traditional balance would be worth after taxes at withdrawal, showing whether the conversion delivers a net benefit over the holding period.
Worked Example: High Earner with $50,000 Pre-Tax IRA
With $50,000 pre-tax Traditional IRA, a $7,000 non-deductible contribution, $10,000 existing Roth, 25% tax rate, 20-year horizon, and 7% returns:
- Total Traditional IRA balance: $50,000 + $7,000 = $57,000
- Pro-rata ratio: $50,000 / $57,000 = 87.7% taxable
- Taxable conversion: $7,000 x 0.877 = $6,140
- Tax liability: $6,140 x 25% = $1,535
- Roth future value (20 yrs at 7%): $17,000 x (1.07)^20 = $65,785
- Traditional after-tax comparison: $50,000 x (1.07)^20 = $193,484 pre-tax, $145,113 after 25% tax
- Tax savings vs traditional: $65,785 - $145,113 = -$79,329 (Traditional wins with this large pre-tax balance)
- Effective conversion cost: $1,535 / $7,000 = 21.9%
The negative result shows a large pre-tax balance makes the conversion costly.
Rolling those funds into a 401(k) first reduces the pro-rata ratio toward zero.
When This Calculator May Understate Your Costs
The calculator does not account for state income taxes — if you live in a state with income tax, your actual tax liability will exceed the displayed amount.
It also assumes a single tax rate throughout; if you expect your rate to change significantly in retirement, model multiple scenarios.
Finally, if you hold SEP or SIMPLE IRA balances in addition to Traditional IRAs, all of those count toward the pro-rata calculation — make sure to include them in the "Traditional IRA Balance Before Conversion" field for an accurate result.
Frequently Asked Questions
What is a backdoor Roth IRA and who should use it?
A backdoor Roth IRA is a legal strategy where high-income earners contribute to a non-deductible Traditional IRA and then convert those funds to a Roth IRA. This bypasses Roth IRA income limits ($161,000 for single filers, $240,000 for married filing jointly in 2025).
How does the pro-rata rule affect a backdoor Roth IRA conversion?
The pro-rata rule requires you to calculate the taxable portion of your conversion based on the ratio of pre-tax to after-tax funds across all your Traditional, SEP, and SIMPLE IRAs. If you have $93,000 in pre-tax IRA funds and convert a $7,000 non-deductible contribution, approximately 93% of the conversion is taxable. Roll pre-tax IRA balances into a 401(k) to avoid this.
Is the backdoor Roth IRA strategy still legal in 2025?
Yes. Despite legislative proposals to eliminate the backdoor Roth IRA strategy, it remains legal as of 2025. The IRS has not issued guidance prohibiting the strategy, and it has been widely used since the income limit on Roth conversions was removed in 2010.
What is the difference between a backdoor Roth IRA and a mega backdoor Roth?
A backdoor Roth IRA involves contributing up to $7,000 (2025) to a Traditional IRA and converting to Roth. A mega backdoor Roth uses after-tax contributions to a 401(k) (up to $69,000 total 401(k) limit in 2025) and converts them to a Roth. The mega backdoor allows significantly larger annual Roth conversions.