The § 408(d)(2) pro-rata rule decides how much of a conversion is taxable — basis comes out tax-free, the rest is ordinary income. No FICA, no self-employment tax.
Line 8 — what moved from traditional to Roth this year.
Last year's line 14 carryforward plus this year's nondeductible contributions.
Line 6 — all traditional, SEP and SIMPLE IRAs combined (§ 408(d)(2)). Zero for a clean backdoor Roth.
Places the conversion in or out of a part-year residence period. Blank = prorated by resident days.
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Taxable amount of the conversion (2025)
$—
Enter the conversion amount to run the 8606 math.
The pro-rata trap
You can't convert "just the basis." § 408(d)(2) aggregates every traditional IRA you own, so a pre-tax balance sitting anywhere makes part of the conversion taxable — the backdoor Roth only works cleanly when the year-end traditional balance is zero.