Roth Conversion Windows (Fill the Bracket, Then Stop)

Updated on November 5, 2025

Use low-income years to move dollars from pre-tax to Roth at a controlled tax rate. Set a ceiling (your top target income) and convert up to it—no higher.

The short version

A Roth conversion window is any year your marginal tax rate is temporarily low (e.g., after retiring but before Social Security or RMDs). Pick a top-of-income ceiling (often the top of a chosen bracket or a personal threshold), convert up to that ceiling, and stop.

Repeat annually until the window closes. Watch for tripwires like healthcare or benefit thresholds.

Mini Roth Conversion Window Calculator

Taxable income this year (before conversions) — $ Your ceiling (top income you won’t exceed) — $ Test conversion amount — $ Current bracket rate on the “room” (%) Next bracket rate for any spillover (%) Expected future marginal rate (%)

Optional thresholds (enter if relevant)

Healthcare/benefit threshold — $ Another threshold — $ Another threshold — $

These are generic placeholders to help you stay under personal limits you care about. Enter your own values as needed.

Room left under your ceiling: $20,000

Of your test conversion: $15,000 fits, $0 spills to next bracket.

Estimated tax on test conversion now: $3,300 (weighted rate 22.0%)

If instead taxed later at 28.0%, simple tax delta: $900 saved by converting this amount now.

Multi-Year Window Planner

Pre-tax balance now (IRA/401k) — $ Target pre-tax balance by window end — $ Years until window closes Assumed annual return on pre-tax (%) Current bracket room per year — $

Estimated annual conversion needed: $84,000 /yr

This uses a simple end-of-year conversion model. Educational only; taxes and benefits vary.

A conversion window only works if the math actually fits your bracket.

If a Roth conversion could change tax brackets, Medicare costs, RMDs, or survivor planning, compare the planning scope and advisor fee in annual dollars before you act.

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How the “window” method works

Pick your ceiling. Choose a maximum total income you won’t cross this year (commonly the top of a target bracket or another personal limit).
Measure the room. Subtract expected income (before conversions) from the ceiling. That’s your max conversion for the year without spillover.
Convert up to the room. If you convert more, the excess is taxed at the next bracket. That may still be fine—just a conscious choice.
Repeat until the window closes. Re-check yearly ceilings as life changes (work, Social Security, RMDs, market moves, healthcare).

Example

You expect $80k income and set a $100k ceiling. Room = $20k. Converting $15k fits completely at your current bracket (e.g., 22%). If you expect to face ~28% later, that $15k conversion now can save roughly 6% × $15k ≈ $900 in lifetime tax on that slice.

Good times to look for a window

Between retirement and when you start Social Security or hit RMD age.
Bridge years (sabbatical, part-time, business loss, unusually large deductions).
Before deferred comp or stock grants begin paying out.

If you’re choosing which dollars to tap while converting, see our quick check: Roth vs Traditional IRA.

Still contributing while converting? Align with your 401(k) Contribution Strategy.

Common questions

Do I need exact tax brackets loaded? No. Pick a ceiling you’re comfortable with and use the calculator to measure room. Enter any personal thresholds you care about.

What about IRMAA/ACA/NIIT/etc.? Treat them as ceilings too. Enter custom thresholds so the calculator warns you if you’d cross them.

The IRMAA ceiling has real numbers now: the 2026 cliffs and the two-year lookback replace the placeholder threshold this calculator asks you to type, and what a conversion costs in 2026 prices the federal, state, and Medicare sides together.

Will conversions affect backdoor Roth contributions? Conversions are separate, but IRA aggregation rules can affect pro-rata calculations on contributions. When in doubt, get personalized advice.

Educational, not tax advice. Your situation may differ—consider professional guidance.

What to do next

Sense-check your ceiling with a fiduciary

Plan conversions across multiple years.

Roth vs Traditional quick check

Pick which dollars to move.

Coordinate with 401(k) contributions

Keep total income under your ceiling.

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See whether an adviser match is worth comparing