Why convert
Converting in a low-income year locks in a lower tax rate on amounts that would otherwise be taxed at higher rates in retirement. Self-employed taxpayers often convert in start-up years with thin profits, or after a year with significant deductions (Section 179, NOL carryforward) that suppress current taxable income.
How the math works
The full amount converted is included in ordinary income for the conversion year. The conversion does not trigger the 10% early-distribution tax, even before age 59½. Converted amounts can be withdrawn from the Roth tax-free immediately, but each conversion has its own five-year clock for the 10% additional tax on early distributions of conversion principal.
Pro-rata rule
When you have both pretax and after-tax dollars in any traditional IRA, conversions are treated as proportionally drawn from each. Backdoor Roth strategies that ignore pre-existing pretax balances often produce surprise taxable income. Consolidating pretax IRA balances into a 401(k) (where allowed by the plan) before converting eliminates the pro-rata problem.
No more recharacterization
Recharacterization (undoing a Roth conversion) is no longer permitted for conversions made after 2017. Plan conversions carefully because they are now irrevocable.
State tax considerations
Most states tax conversions the same way as federal, but rules vary. A few states (Pennsylvania, Mississippi) treat retirement income differently and may have favorable conversion rules.
Penalties for late or missing filings
Late or missing filings of Roth IRA Conversion (reported on Form 8606) draw distinct penalties depending on the form: failure-to-file (5% per month, capped at 25%), failure-to-pay (0.5% per month), failure-to-deposit for payroll forms (graduated based on lateness), failure-to-file information returns (per-return penalty that scales with size and lateness), and accuracy-related penalties (20% of underpayment for negligence or substantial understatement). The dollar amounts are not trivial. Calendaring the form's deadline, setting up an electronic reminder a week in advance, and using a payroll or tax-prep service that auto-files are the cheapest defenses against accidental late filings.
What it does not cover
Roth IRA Conversion (reported on Form 8606) does not stand alone — it lives inside a small ecosystem of supporting forms, schedules, and elections that together carry the full weight of a small-business return. Knowing what Roth IRA Conversion (reported on Form 8606) does not handle is just as important as knowing what it does. The instructions list the cross-references explicitly: items computed elsewhere (Schedule C net profit, Schedule SE self-employment tax, Form 4562 depreciation), items reported on a separate form (Form 8829 home office, Form 1099-NEC information returns), and items handled by an entirely different return entirely (Form 1120-S for S-corps, Form 1065 for partnerships). Drawing the boundary cleanly avoids double-counting and avoids leaving deductions on the table.