About the Backdoor Roth IRA Calculator
A backdoor Roth is a two-step move for people whose income is too high to contribute to a Roth IRA directly: make a nondeductible contribution to a traditional IRA, then convert it to a Roth. This calculator works out how much of that conversion is taxable, following the same steps as IRS Form 8606, Part I and Part II.
The key is the pro-rata rule. The IRS treats all of your traditional, SEP and SIMPLE IRAs as one pot, so if you hold pre-tax IRA money, only a fraction of any conversion is tax-free — even if you convert only the new after-tax contribution. Enter your nondeductible contribution, any basis from earlier years, the amount you convert and the value of all your traditional, SEP and SIMPLE IRAs on 31 December after the conversion.
For 2026 the IRA contribution limit is $7,500 ($8,600 if you are 50 or older), and direct Roth contributions phase out between $153,000 and $168,000 of modified AGI for single filers and $242,000–$252,000 for married couples filing jointly. Employer 401(k) and 403(b) balances do not count toward the pro-rata calculation, which is why many people roll pre-tax IRA money into a workplace plan before doing a backdoor Roth.
With the default inputs, the taxable part of the conversion is $0.00. Change any value above to recalculate instantly.
How to use the backdoor roth ira calculator
- 1Enter the nondeductible amount you contributed to a traditional IRA this year.
- 2Add any basis left from earlier years, shown on last year’s Form 8606.
- 3Enter the amount you converted to Roth, including any earnings.
- 4Enter the 31 December value of all your traditional, SEP and SIMPLE IRAs after the conversion.
- 5Review the taxable amount and the estimated tax, then consider rolling pre-tax IRAs into a 401(k) first.
Formula and method
Form 8606 adds your nondeductible contribution for the year to any basis from earlier years (line 3). It then divides that basis by the total of your year-end traditional, SEP and SIMPLE IRA value, other distributions and the amount converted (lines 6–9), capped at 100% (line 10). That fraction of the conversion is tax-free; the rest is ordinary income.
The year-end value is measured on 31 December after the conversion, so a pre-tax rollover IRA you open later in the same year still dilutes the ratio. Basis not used this year carries forward. The tax cost multiplies the taxable amount by the marginal rate you enter and ignores any effect on credits, deductions or IRMAA.
- Basis
- Nondeductible contributions not yet recovered (Form 8606 line 3)
- Dec 31 value
- All traditional, SEP and SIMPLE IRAs after the conversion
- Conversion
- Amount moved to a Roth IRA this year
Worked examples
Clean backdoor Roth with no other IRAs
You contribute $7,500 after tax and convert it before it earns anything. With no other traditional IRA money on 31 December, the tax-free fraction is 7,500 ÷ 7,500 = 100%, so nothing is taxable.
Pro-rata trap: $50,000 rollover IRA
With $50,000 of pre-tax money in a rollover IRA, the fraction is 7,500 ÷ (50,000 + 7,500) = 13.04%. Only $978 of the conversion is tax-free and $6,522 is taxable — about $1,565 at 24%. The unused $6,522 of basis carries forward.
Age 50+ with $8,700 converted after small gains
An $8,600 contribution earned $100 before conversion. The fraction is 8,600 ÷ 8,700 = 98.85%, so $8,600 of the conversion — the full basis — is tax-free and only the $100 of earnings is taxed — $32 at a 32% rate.
Frequently asked questions
What is the pro-rata rule for backdoor Roth conversions?+
The IRS treats all your traditional, SEP and SIMPLE IRAs as one account when you convert. The tax-free share of any conversion equals your after-tax basis divided by the total value of those IRAs at year end plus the amounts converted and distributed. You cannot choose to convert only the after-tax dollars.
Do 401(k) balances count toward the pro-rata rule?+
No. Only traditional, SEP and SIMPLE IRAs are included on Form 8606. Money in a 401(k), 403(b), 457(b) or the Thrift Savings Plan does not count, so rolling pre-tax IRA money into a workplace plan that accepts roll-ins can make a backdoor Roth fully tax-free.
Which form reports a backdoor Roth?+
Form 8606. Part I reports the nondeductible contribution and figures the taxable part of any distributions; Part II reports the conversion. You also receive Form 1099-R from the IRA custodian showing the conversion as a distribution.
Who needs a backdoor Roth in 2026?+
Direct Roth IRA contributions phase out between $153,000 and $168,000 of modified AGI for single filers and between $242,000 and $252,000 for married couples filing jointly in 2026. Above those levels, a nondeductible traditional IRA contribution followed by a conversion is the main way in.
Is the backdoor Roth legal?+
Yes. Anyone with earned income can make a nondeductible traditional IRA contribution, and there have been no income limits on Roth conversions since 2010. The key is to report both steps correctly on Form 8606 and to understand how the pro-rata rule applies to any other IRA money you hold.
Tax results are estimates based on published rules and simplified assumptions. They are not tax advice — check official guidance or a tax professional for your situation.