The Roth Conversion Window Most People Don't Notice Until It's Closing

There's a stretch of years in many retirements when taxable income quietly drops to the lowest level it will ever be: after the paychecks stop, before Social Security begins, and before required minimum distributions force money out of your IRA whether you want it or not.

Tax planners call it the conversion window. Money moved from a traditional IRA to a Roth during those years can be taxed at 10%, 12%, or 22% — money that, left alone until RMDs stack on top of Social Security later, might come out at 24% or more. Same dollars, different toll simply because of when they cross the bridge.

What a conversion actually is

A Roth conversion moves money from a pre-tax account (traditional IRA, old 401(k)) into a Roth IRA. The amount converted is added to your ordinary income for the year, and you pay tax on it now. In exchange:

• The money grows tax-free from then on, and qualified withdrawals are tax-free.
• Roth IRAs have no RMDs during your lifetime — the IRS never forces the money out.
• Heirs generally inherit Roth dollars income-tax-free (most must still empty the account within 10 years).

A conversion is not a contribution — there's no income limit and no annual cap. The only limiter is your tolerance for the tax bill.

The bracket-filling framework

The standard approach is disarmingly simple: convert enough to fill your current bracket, and stop.

Say a married couple retires at 63 with $45,000 of taxable income. The 12% bracket runs to $100,800 (2026). They have roughly $55,000 of "room" that will be taxed at just 12% — room that expires December 31 and resets next year. Converting $55,000 costs about $6,600 in federal tax. If that money would otherwise come out at 24% during RMD years, the same withdrawal would have cost $13,200.

Repeat for each year of the window and a meaningful slice of the IRA crosses at low rates. The Roth Conversion calculator does exactly this math — showing which brackets a conversion fills and how much room is left in your target bracket.

The trapdoors

Conversions raise your modified adjusted gross income, and several rules key off that number:

• Medicare IRMAA. Premium surcharges use a two-year lookback and are cliffs — one dollar over a threshold ($218,000 joint in 2026) raises both spouses' premiums for a full year, two years later. Large conversions at 63+ deserve a check against the tiers.
• Social Security taxation. If you're already collecting, a conversion can pull more of your benefit into taxable income in that year.
• ACA subsidies. Retiring before 65 with marketplace coverage? Conversion income reduces premium credits — sometimes enough to erase the conversion's benefit.
• Paying the tax. Conversions work best when the tax is paid from cash outside the IRA, letting the full converted amount keep compounding.

Who should hesitate

Conversions aren't automatic wins. If your retirement tax rate will likely be lower than today's — modest balances, no pension, generous standard deduction — converting now can mean overpaying. Charitable plans matter too: pre-tax IRA dollars given through qualified charitable distributions, or left to charity at death, may never be taxed at all.

The honest summary: conversions are a bet that today's known rate beats tomorrow's likely one. In the window years, that bet is often — not always — attractive. Model it with the calculator, then pressure-test the full picture with a tax professional before pulling the trigger.