Americans with money in a traditional IRA or 401k can lock in today’s tax rates on retirement money that would otherwise be taxed at a much higher rate under required minimum distributions decades from now.

The 2026 inflation-adjusted brackets allow for conversions to happen at slightly higher levels, with the 12% ceiling at $100,800 for married filers and the 24% ceiling at $403,550. That extra headroom matters when you’re trying to move pretax retirement dollars into a Roth account without pushing yourself into the next tax bracket.

What follows uses those 2026 brackets as targets, with three worked scenarios for readers still in the workforce. It also covers two traps (Medicare IRMAA and ACA premium tax credits) that can quietly erase the savings.

What "Filling Up A Bracket" Actually Means

A Roth conversion moves money from a traditional retirement account (such as a 401(k) rollover IRA) into a Roth IRA. The converted amount is added to your ordinary income for the year. You pay tax on it at your marginal rate. Once inside the Roth, the money grows tax-free and qualified withdrawals after age 59½ are tax-free.

“Filling up a bracket” means converting exactly enough to reach (but not exceed) the top of a specific tax bracket. Go one dollar past, and every additional dollar gets taxed at the next rate up.

Here are the 2026 tax brackets:

The 2026 standard deduction is $16,100 for single filers and $32,200 for married filing jointly.

Your target bracket depends on the rate you expect to pay in retirement. Converting at 12% today when you expect the 22% or 24% bracket later is a straightforward win. Converting at 32% when you might drop to 22% later is a loss.

Most pre-retirees focus on the 12% and 24% ceilings because the jumps above them (to 22% and 32%) are the steepest cliffs in the bracket structure.

Three Scenarios

Scenario A — The Sabbatical Year

Mark and Samantha, both 56, married filing jointly. Samantha took an unpaid sabbatical. Household W-2 income for 2026: $90,000.

After the $32,200 standard deduction, taxable income before any conversion is $57,800. That leaves $43,000 of space before they hit the top of the 12% bracket at $100,800.

If they convert $43,000 from Mark’s rollover IRA, their taxable income rises to exactly $100,800. The incremental federal tax on the conversion is $43,000 × 12% = $5,160. Their all-in federal tax on the full $100,800 climbs from $6,440 to $11,600, which is a $5,160 difference that matches the marginal math.

Had they pushed another $10,000 into the 22% bracket, that last $10,000 would cost $2,200 in tax instead of $1,200, which is a 10% penalty on the overflow. Stopping at the ceiling keeps every converted dollar at 12%.

Scenario B — The Laid-Off Single Filer

Jenna, 48, single, was laid off in March. She earned $25,000 through March plus a $10,000 severance, bringing her 2026 earned income to $35,000. She is living on savings and has an old 401(k) she rolled into a traditional IRA worth $400,000.

After her $16,100 standard deduction, taxable income before conversion is $18,900. She has $31,500 of room before the top of the 12% bracket at $50,400.

Converting $31,500 costs her $3,780 in federal tax (12% marginal). That same slice of dollars taxed in retirement at 22% would cost $6,930, which is a $3,150 savings on this block alone, before any tax-free Roth growth over the next two decades.

She could push further into the 22% bracket, but each additional dollar now costs 22 cents of federal tax. Whether that is worth it depends on whether she expects to retire in the 22%, 24%, or higher bracket.

For most middle-income savers, stopping at the 12% line is the conservative call.

Scenario C — High Earners Filling the 24% Ceiling

Dan and Mia, both 54, married, both working. Household AGI: $320,000. They are peak earners with a combined $1.8 million in pretax 401(k) balances that will drive large RMDs starting at age 75.

After the $32,200 standard deduction, taxable income before conversion is $287,800, which is already in the 24% bracket. The top of the 24% band for MFJ in 2026 is $403,550, giving them $115,750 of headroom before the 32% bracket kicks in.

If they convert $115,750 from Dan’s rollover IRA, the incremental federal tax is $115,750 × 24% = $27,780. Their total federal tax on $403,550 of taxable income is $82,048, up from $54,268. Again, a $27,780 delta that confirms the entire conversion stayed inside the 24% band.

The planning case: if their pretax balances grow to $3.5 million by age 75, RMDs alone could push taxable income to $450,000-plus in today’s dollars, well into the 32% bracket under current law. Paying 24% now on a block of that money saves 8 percentage points against those future RMDs, which is roughly $9,260 per $115,750 block of conversion, before factoring in tax-free Roth growth.

Consumer Impact: The IRMAA and ACA Traps Most People Miss

Federal tax brackets are only one part of the picture. Conversions raise your modified adjusted gross income (MAGI), and two separate cliff systems use MAGI as a trigger.

Medicare IRMAA. Once either spouse turns 65 and enrolls in Medicare, Part B and Part D premiums are surcharged based on MAGI from two years earlier. For 2026, the first IRMAA surcharge hits single filers with 2024 MAGI above $106,000 and married filers above $212,000 and the tiers climb from there. A conversion done at age 63 will influence IRMAA at age 65.

A conversion done at 53 will not, but aggressive late-50s and early-60s conversions can push future IRMAA higher unless modeled carefully.

ACA premium tax credits. Pre-retirees not on employer coverage (including someone on a sabbatical or between jobs) may be buying ACA marketplace plans with income-based subsidies. Conversion income counts toward MAGI for ACA purposes, and the premium tax credit phaseout was restructured after the enhanced subsidies expired at the end of 2025.

A conversion that nudges MAGI past the phaseout can claw back thousands of subsidy dollars, which often outweighs the federal tax savings. Jenna in Scenario B should model her 2026 ACA MAGI before converting, as a smaller conversion may net out better once subsidies are factored in.

Action Steps

If you're thinking about filling your brackets with Roth conversions, here's what to know:

1. Project your 2026 taxable income before December, subtracting the standard deduction, to pinpoint exactly how much room you have to each bracket ceiling.
2. Decide which bracket ceiling (12%, 22%, or 24%) you are targeting based on your expected retirement tax rate, not today’s rate.
3. Estimate IRMAA exposure if either spouse is within two years of age 65, and ACA subsidy impact if you are buying a marketplace plan.
4. Execute the conversion before December 31 (the deadline is calendar-year, not tax-filing-year) and pay the tax from non-retirement funds so the full converted amount lands inside the Roth.
5. Recheck annually. A single low-income year (sabbatical, severance, business loss, between-jobs stretch) is often the single best conversion window you will get.

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