IRA Pro-Rata Rule & Form 8606 Calculator
Enter your IRA basis, year-end IRA value, distributions, and Roth conversions to estimate the Form 8606 pro-rata split. The result shows the taxable conversion amount, recovered basis, carryforward basis, and a line summary you can compare with the form.
Taxable portion of Roth conversions$6,510.00
- Total IRA basis before line 4 adjustment
- $7,000.00
- Basis available for this year's allocation
- $7,000.00
- Pro-rata denominator
- $100,000.00
- Nontaxable percentage
- 7%
- Nontaxable portion of regular distributions
- $0.00
- Taxable portion of regular distributions
- $0.00
- Nontaxable portion of Roth conversions
- $490.00
- Basis carried forward
- $6,510.00
- Estimated federal income tax
- $1,562.40
Form 8606 line summary
| Line | Value | What it represents |
|---|---|---|
| 1 | $7,000.00 | Nondeductible traditional IRA contributions |
| 2 | $0.00 | Total basis from prior Forms 8606 |
| 3 | $7,000.00 | Line 1 plus line 2 |
| 4 | $0.00 | Line 1 contributions made after December 31 |
| 5 | $7,000.00 | Basis available for the pro-rata allocation |
| 6 | $93,000.00 | December 31 IRA value plus outstanding rollovers |
| 7 | $0.00 | Other traditional, SEP, and SIMPLE IRA distributions |
| 8 | $7,000.00 | Net amount converted to Roth IRAs |
| 9 | $100,000.00 | Line 6 plus lines 7 and 8 |
| 10 | 0.070 | Nontaxable decimal used on the form |
| 11 | $490.00 | Nontaxable part of Roth conversions |
| 12 | $0.00 | Nontaxable part of other distributions |
| 13 | $490.00 | Total basis recovered this year |
| 14 | $6,510.00 | Basis carried forward |
| 15a | $0.00 | Regular distributions before special adjustments |
| 15b | separate treatment | Qualified disaster and similar adjustments are not modeled |
| 15c | $0.00 | Taxable regular distributions before omitted adjustments |
| 16 | $7,000.00 | Gross Roth conversions |
| 17 | $490.00 | Nontaxable conversion amount from line 11 |
| 18 | $6,510.00 | Taxable Roth conversion amount |
Uses the entered traditional, SEP, and SIMPLE IRA amounts for one taxpayer only.
Special Form 8606 adjustments are shown as separate treatment in the line summary.
How to use this calculator
- Enter your prior-year Form 8606 basis and this year's nondeductible traditional IRA contribution.
- Separate any part of that contribution made after December 31 for the tax year.
- Enter the year-end value of your own traditional, SEP, and SIMPLE IRAs, plus any outstanding rollovers.
- Enter regular IRA distributions and Roth conversions using gross amounts before withholding.
- Review the taxable conversion, carryforward basis, and Form 8606 line summary.
How the pro-rata amount is calculated
Form 8606 does not let you choose that a Roth conversion came only from after-tax IRA dollars when you also own pre-tax traditional, SEP, or SIMPLE IRA money. The form aggregates the taxpayer's counted IRAs and uses one fraction to decide how much of the year's distributions and conversions is nontaxable.
The calculator follows the core Part I and Part II sequence:
total basis = prior-year basis + current-year nondeductible contributions
available basis = total basis - line 1 contributions made after December 31
denominator = December 31 counted IRA value + outstanding rollovers + regular distributions + Roth conversions
line 10 ratio = available basis / denominator, rounded to three decimal places and capped at 1.000.
The nontaxable part of regular distributions is line 7 multiplied by the line 10 ratio. The nontaxable part of Roth conversions is line 8 multiplied by the same ratio. The taxable conversion amount, generally Form 8606 line 18, is the gross Roth conversion minus the nontaxable conversion amount. The basis carried forward is total basis minus basis recovered through both regular distributions and conversions.
What moves the result
The December 31 IRA balance often changes the answer more than the conversion itself. A backdoor Roth conversion done in March is still tested against the value of counted IRAs at year end. Moving pre-tax IRA money into or out of a counted IRA before December 31 can therefore change the nontaxable percentage, subject to the rules that apply to the actual transaction.
Line 4 also matters. A contribution made in January through the filing deadline for the prior tax year can be reported on line 1, but it is removed from the current-year allocation. That basis can remain available for a later year rather than sheltering distributions from the year just ended.
What this calculator leaves out
This is a basic Form 8606 allocation tool. It does not decide whether an IRA contribution was deductible, permitted, or within the annual limit. It also does not model returned contributions, recharacterizations, qualified charitable distributions, disaster distributions, repayments, inherited IRAs, Roth IRA distributions, penalties, withholding, state tax, credits, phaseouts, or full tax-bracket calculations. Reconcile the entries to Forms 1099-R and 5498 and to any prior Forms 8606 showing basis.
Worked example
Suppose you have no prior Form 8606 basis, make a $7,000 nondeductible traditional IRA contribution during the tax year, convert $7,000 to a Roth IRA, and still have $93,000 in counted traditional, SEP, and SIMPLE IRAs on December 31. There are no other distributions or outstanding rollovers.
Total basis is $7,000. The denominator is $93,000 + $7,000, or $100,000. The Form 8606 line 10 ratio is $7,000 / $100,000 = 0.070, so 7% of the $7,000 conversion is nontaxable. The nontaxable conversion amount is $490, the taxable conversion amount is $6,510, and $6,510 of basis carries forward. At a 24% marginal federal rate, the simplified federal tax estimate is $1,562.40.
Common questions
What accounts count under the IRA pro-rata rule?
For this calculation, count the taxpayer's own traditional IRAs, SEP IRAs, and SIMPLE IRAs. Do not include Roth IRAs, inherited IRAs, 401(k), 403(b), TSP, or other workplace-plan balances. A spouse runs a separate calculation for that spouse's own IRAs.
How do Form 8606 lines 6, 7, 8, and 9 work together?
Line 6 is the year-end value of counted IRAs, including outstanding rollovers required by the instructions. Line 7 is other IRA distributions, and line 8 is Roth conversions. Line 9 adds those amounts to create the denominator for the nontaxable percentage.
Why does a December 31 IRA balance affect an earlier Roth conversion?
The form uses the aggregate value of counted IRAs at the end of the year, not the account balance on the conversion date. That is why a conversion completed earlier in the year can still be partly taxable if pre-tax IRA money remains in a counted IRA on December 31.
How are contributions made after December 31 treated?
A contribution made after December 31 but designated for the prior tax year can appear on Form 8606 line 1. Line 4 removes that amount before the year's pro-rata allocation, so it does not shelter distributions or conversions from the year that just ended.
Can unused nondeductible IRA basis carry forward?
Yes. Basis that is not recovered through the year's distributions and conversions remains on Form 8606 line 14. That carryforward basis can be used in later-year Form 8606 calculations.
Why might tax software differ from this estimate?
Tax software may apply details this calculator does not model, including special distribution adjustments, returned contributions, disaster rules, repayments, or recharacterizations. It may also keep more decimal places in intermediate steps before producing form entries.