Backdoor Roth IRA & Pro-Rata Rule Calculator
Determine exact taxable vs tax-free Roth conversion amounts, calculate Form 8606 liabilities, and model 401(k) reverse rollover shelters.
1. Current Year Non-Deductible Contribution
2. Existing Pre-Tax IRA Balances
Dec 31 SnapshotUnder IRC § 408(d)(2), the IRS sums all your Traditional, Rollover, SEP, and SIMPLE IRAs across all brokerages (Vanguard, Fidelity, Schwab, etc.) as of Dec 31.
3. Tax Bracket & Reverse Rollover
Simulate rolling all pre-tax IRA funds into an employer 401(k) before Dec 31 to zero out pre-tax balances and eliminate pro-rata taxes.
Backdoor Roth Tax Breakdown
$942
13.5% Tax-Free$6,058
86.5% Taxable$1,757
Fed + State Tax$6,058
Carried to Line 14Conversion Composition & Tax Drag
Form 8606 Visual BreakdownIRS Form 8606 Line-by-Line Mapping
| Line | Form 8606 Description | Value |
|---|---|---|
| Line 1 | Current year non-deductible contribution | $7,000 |
| Line 2 | Total unrecovered basis from prior years | $0 |
| Line 3 | Total non-deductible basis (Line 1 + Line 2) | $7,000 |
| Line 6 | Value of all Traditional, SEP, & SIMPLE IRAs on Dec 31 | $45,000 |
| Line 8 | Net amount converted to Roth IRA in tax year | $7,000 |
| Line 11 | Non-taxable portion of Roth conversion | $942 |
| Line 18 | Taxable amount to report on Form 1040 (Line 4b) | $6,058 |
Click "Run Private AI Tax Audit" to evaluate potential Pro-Rata tax traps, Form 8606 basis carryforwards, and step-by-step 401(k) reverse rollover instructions. Your data is 100% private to you—zero server access.
Zero Data Access: All tax numbers and account balances are evaluated 100% locally in your browser. Zero Server Access
The $50,000 Rollover IRA Trap: How a Backdoor Roth Triggered a Surprise $2,300 Tax Bill
A real-world tax audit breakdown of the IRS Form 8606 Pro-Rata Rule and how executing a 401(k) reverse rollover eliminated the tax penalty completely.
The Pro-Rata Rule Explained Simply
High earners exceeding IRS Roth income limits ($165,000 Single / $246,000 Married in 2026) use the Backdoor Roth IRA strategy: contribute non-deductible cash to a Traditional IRA, then immediately convert it to a Roth IRA. However, if you possess any existing pre-tax IRA money (such as an old 401k rolled into a Traditional IRA), the IRS forbids you from converting only your non-deductible contribution. Under IRC § 408(d)(2), the conversion is taxed proportionally across your entire aggregated IRA pool.
The Scenario: Rachel's $220,000 Tech Income
Rachel earns $220,000 as a Senior Product Manager. Four years ago, she rolled over an old $50,000 401(k) from a previous employer into a Vanguard Traditional Rollover IRA. In 2026, she makes a $7,000 non-deductible Traditional IRA contribution and converts it to a Roth IRA, assuming it will be 100% tax-free:
Total IRA Pool: $57,000
Tax-Free Ratio: 12.28% ($860)
Taxable: $6,140 (Owes $2,088 Tax!)
Roll $50k into: Active Employer 401(k)
Dec 31 Pre-Tax Balance: $0.00
401(k) funds exempt from Form 8606!
Tax-Free Ratio: 100.0% ($7,000)
Tax Due: $0.00 (Pure Tax-Free!)
Saved $2,088 in unnecessary income tax.
Form 8606 Pro-Rata Math Comparison
| Strategy | Pre-Tax IRA (Dec 31) | Roth Conversion | Tax-Free Portion | Taxable Portion | Tax Due @ 34% |
|---|---|---|---|---|---|
| With $50k Rollover IRA (No Fix) | $50,000 | $7,000 | $860 (12.3%) | $6,140 (87.7%) | $2,088 |
| With 401(k) Reverse Rollover | $0.00 (Zeroed) | $7,000 | $7,000 (100%) | $0.00 (0%) | $0.00 (Clean) |
The Golden Rule of Backdoor Roths
To execute a clean, 100% tax-free Backdoor Roth IRA, your total aggregate balance in all Traditional, Rollover, SEP, and SIMPLE IRAs across all financial institutions must equal $0.00 on December 31st of the conversion year. If you have pre-tax IRA dollars, execute a Reverse Rollover into your current employer 401(k) or Solo 401(k) first.
Frequently Asked Questions (Backdoor Roth & Pro-Rata Rule)
What is the Backdoor Roth IRA Pro-Rata Rule?
The IRS Pro-Rata Rule (IRC Section 408(d)(2)) mandates that when you convert funds from a Traditional IRA to a Roth IRA, the IRS treats all your pre-tax IRA accounts (Traditional, SEP, and SIMPLE IRAs) as a single aggregated pool. You cannot selectively convert only your non-deductible contribution; the conversion is taxed proportionally based on the ratio of pre-tax to after-tax dollars.
What date does the IRS look at for the Pro-Rata Rule balance?
The IRS calculates your pre-tax IRA balance as of December 31st of the calendar year in which the Roth conversion takes place, not the balance on the day you executed the conversion.
How can I eliminate the Pro-Rata Rule tax on a Backdoor Roth?
You can eliminate the pro-rata tax by executing a 'Reverse Rollover'—rolling over all existing pre-tax Traditional, Rollover, and SEP IRA funds into an employer-sponsored 401(k) or Solo 401(k) before December 31st. Because employer 401(k) plans are qualified under IRC Section 401(a), they are excluded from Form 8606 calculations, resetting your IRA pre-tax balance to zero.
Do Roth 401(k) or traditional 401(k) balances trigger the Pro-Rata Rule?
No. Traditional 401(k), Roth 401(k), 403(b), and 457(b) balances are completely excluded from the IRA Pro-Rata calculation. Only Traditional IRAs, Rollover IRAs, SEP IRAs, and SIMPLE IRAs are counted.