Backdoor Roth Calculator: Estimate Conversion Taxes and Long-Term Value
Use this guide to understand the assumptions, inputs, results, and next steps behind the calculator.
Created by Luis Gonzalez · Last updated May 2, 2026
A backdoor Roth IRA is a two-step strategy: contribute to a traditional IRA and convert the contribution to a Roth IRA. It can help higher-income savers build Roth assets even when their income is above the direct Roth IRA contribution phaseout. The tradeoff is that a conversion may create current income tax, especially if you have other untaxed money in traditional, SEP, or SIMPLE IRAs.
This calculator estimates the tax on conversion, projects Roth growth, and compares it with a taxable-account estimate. With the default inputs, it projects $507,574 in the Roth at retirement and a $98,976 net advantage over the modeled taxable alternative. These are projections, not guarantees: investment returns, tax rates, account rules, and the calculator’s simplifying assumptions all affect the result.
To compare Roth-account approaches, you can also use the Roth IRA Tax Calculator and Mega Backdoor Roth Calculator. A Roth workplace plan may offer another route; see the Roth 401(k) Calculator or Roth 403(b) calculator.
Run the estimate with your own IRA balances
Enter your age, intended retirement age, annual income, filing status, state tax rate, expected return, and expected retirement tax rate. Add the amount you plan to contribute and the balance in your existing traditional IRAs. The calculator uses the existing IRA balance to estimate the pro-rata rule’s effect.
The years to convert input determines how many years of contributions are included, up to the years remaining before retirement. The optional Mega Backdoor Roth inputs are separate from the regular IRA calculation; explore that workplace-plan strategy with the Mega Backdoor Roth Calculator.
Check the calculator’s contribution limit against current IRS rules before contributing. The result uses a modeled maximum contribution of $7,500 for the default age. Contribution limits and catch-up rules are set by tax law and can change. The IRS explains IRA contribution eligibility and limits at irs.gov/retirement-plans/ira-deduction-limits.
The pro-rata rule can turn a “nondeductible” contribution into a taxable conversion
A nondeductible contribution is made with after-tax money, but that does not automatically make every dollar converted tax-free. When you convert, the IRS generally considers the value of your traditional, SEP, and SIMPLE IRAs together. The conversion is treated as partly pre-tax and partly after-tax if those accounts contain a mix of tax bases.
The calculator approximates this with a pro-rata percentage based on your existing traditional IRA balance and the new contribution. For example, a zero existing IRA balance produces a 0% pro-rata percentage in the default calculation, so the full $7,500 contribution is treated as nontaxable and the estimated conversion tax is $0. That is why the default result does not show an immediate tax bill.
If you have a large pre-tax IRA, the taxable share can rise. A workplace plan that accepts incoming rollovers may sometimes provide an option to move eligible pre-tax IRA assets out of the IRA before converting, but plan terms and tax rules matter. A 401(k)-to-Roth IRA conversion calculator is for a different transaction; do not assume that moving money directly to a Roth has the same tax result as a rollover to a workplace plan.
The IRS requires taxpayers to report IRA contributions and conversions on the relevant tax forms, including Form 8606 when applicable. Keep records of nondeductible basis so that after-tax contributions are not taxed a second time. Review the current IRS Form 8606 instructions.
What the default projection says—and what it leaves out
The default assumptions are age 35, retirement at 60, $200,000 of annual income, a single filing status, a 5% state tax rate, $7,500 of annual contributions, no existing traditional IRA balance, a 7% return, and 25 years of conversions. The calculator identifies a 24% federal marginal rate from its income estimate. In the default case, the pro-rata tax calculation is zero because the existing IRA balance is zero.
The projection’s key result is $507,574 at retirement. The calculator also models a taxable alternative at $408,598, then calculates a $98,976 net advantage after subtracting current conversion taxes. Its taxable-account comparison applies a 15% tax to investment growth each year. It is a simplified comparison, not a personalized forecast of a real brokerage account’s taxes.
The inflation-adjusted Roth value is $273,781 in today’s dollars under the calculator’s 2.5% inflation assumption. Nominal dollars show the account balance in the future; real dollars help compare that amount with today’s purchasing power. For other ways to build or evaluate Roth savings, compare the Roth IRA Tax Calculator with the IRA Calculator.
| Scenario | Contribution and existing IRA balance | Conversion tax in the calculator | What changes |
|---|---|---|---|
| Default: no pre-tax IRA balance | $7,500 contribution; $0 existing balance | $0 | The model assigns no taxable share to the conversion. |
| Existing IRA balance equals contribution | $7,500 contribution; $7,500 existing balance | Half the contribution is taxable | The pro-rata percentage is 50%, so the taxable conversion amount is $3,750 before applying the tax rate. |
| Existing IRA balance is four times contribution | $7,500 contribution; $30,000 existing balance | Most of the contribution is taxable | The pro-rata percentage is 80%, so the taxable conversion amount is $6,000 before applying the tax rate. |
The last two rows illustrate the calculator’s proportional method, not an official tax calculation for a specific return. Actual Form 8606 calculations use year-end IRA values and other details, so compare the estimate with your full account picture.
The math behind the result cards
The model estimates the taxable share of the conversion from the existing traditional IRA balance and the contribution. It then applies the estimated combined federal and state marginal rate to that taxable amount.
Actual contribution = the smaller of planned contribution and modeled contribution limit
Pro-rata percentage = existing traditional IRA balance / (existing balance + actual contribution)
Taxable conversion = actual contribution × pro-rata percentage
Conversion tax = taxable conversion × (federal marginal rate + state rate)
For the default case, the taxable conversion is $7,500 × 0% = $0. The estimated federal marginal rate is 24%, and the state rate is 5%, but the combined rate applies to zero taxable conversion dollars, so $0 × 29% = $0 tax.
The account projection adds each annual contribution and applies the expected return. In the first projected year, ($0 + $7,500) × 1.07 = $8,025. After 25 annual contributions, the projected Roth balance is $507,574. The model’s taxable comparison is $408,598, so the net advantage is $507,574 − $408,598 − $0 = $98,976.
This calculation assumes a steady annual return, rather than modeling the sequence of market gains and losses. It also does not determine whether a contribution is deductible, whether a conversion is legally eligible, or whether qualified Roth withdrawal requirements will be met. For a broader comparison of tax treatments, see Roth IRA vs. Traditional IRA: Which Saves More Taxes?.
Compare the strategy with other retirement-account choices
A backdoor Roth can be useful when direct Roth IRA contributions are restricted by income, but it is not automatically the best choice for every saver. Paying conversion tax now can be less attractive if the taxable portion is large or if you expect a lower tax rate later. Paying tax on a small or zero taxable conversion may be easier to justify if you value Roth treatment and can leave the money invested for many years.
A workplace plan may allow after-tax contributions and Roth conversions under a separate set of plan rules. That is the subject of the Mega Backdoor Roth Calculator. If you are comparing Roth and pre-tax workplace savings, use the Roth 401(k) Calculator alongside your IRA estimate.
Age also matters. The model adds a catch-up amount for people age 50 or older, but contribution limits are adjusted periodically. A contribution is also limited by compensation and other eligibility rules. Check the current IRS limit before acting rather than relying on a prior year’s limit. Roth contributions are not the same as conversions, and conversion income can have tax consequences even when the original contribution was nondeductible.
For a longer-term plan, compare this estimate with your wider retirement projection using a retirement needs calculator or a 401(k) compound interest calculator. If you want to see how an IRA withdrawal might be taxed, use the IRA Withdrawal Calculator and IRA early withdrawal penalty calculator.
Frequently asked questions
Is a backdoor Roth contribution illegal?
No, a backdoor Roth is generally a lawful contribution-and-conversion strategy when carried out under the tax rules, but the conversion can be taxable and must be reported correctly. The IRS provides instructions for reporting nondeductible IRA contributions and conversions on Form 8606.
Does a high income prevent me from using this strategy?
High income can restrict direct Roth IRA contributions, but it does not by itself mean that a traditional IRA contribution and Roth conversion are unavailable. Eligibility, deductibility, account balances, and tax reporting still matter. The calculator flags income above its modeled Roth limit; it does not decide your legal eligibility.
Why can an existing traditional IRA create a tax bill?
The pro-rata rule generally treats traditional, SEP, and SIMPLE IRA balances together when determining what share of a conversion is taxable. A balance in another IRA can make part of a conversion taxable even if the new contribution itself was nondeductible.
Should I convert now or wait until retirement?
That depends on the tax rate applied now versus the rate that would apply to future withdrawals, plus how much pre-tax IRA money you have. Converting now can create an upfront tax cost; waiting may preserve tax deferral but leave future withdrawals taxable. Test different state and retirement tax assumptions rather than treating one projection as a recommendation.
Does a Roth IRA have required minimum distributions for the original owner?
Roth IRAs generally do not require lifetime distributions for the original owner. Beneficiaries can face distribution requirements after inheriting the account. See the inherited IRA calculator for a separate inherited-account estimate.
Can I use conversion money immediately?
A conversion is not the same as a contribution, and early access can have tax and penalty consequences depending on the account, age, and timing. Check the rules before using converted assets as short-term cash; the Roth IRA early withdrawal penalty calculator can help explore one aspect of early withdrawals.
Next steps for a more reliable estimate
First, list all traditional, SEP, and SIMPLE IRA balances that may affect the pro-rata calculation. Then verify the current contribution limit, document after-tax basis, and test a range of investment returns and retirement tax rates. Use the Roth IRA MAGI calculator to check direct-contribution income rules, and compare this result with other retirement assets in a retirement calculator. The estimate is a planning aid; the tax forms and your complete account balances determine the actual tax treatment.