Roth Conversion After IRA Rollover: Should You Convert — And How Much?

You've rolled your 401(k) into a traditional IRA. Now what? For many people, a freshly rolled IRA creates one of the best Roth conversion opportunities they'll ever have — a large pre-tax balance, often during a temporarily lower-income year, with decades for Roth growth to compound tax-free. But converting too much in one year can trigger a costly Medicare surcharge, push income into a higher bracket, or create a cash-flow crunch paying the tax bill. Here's how to think through it systematically.

Why the rollover moment creates a conversion opportunity

The year you leave a job and roll your 401(k) is often unusual income-wise. You may have partial-year employment income, a severance payout that ends, or you're transitioning into retirement entirely. That creates a potential gap between now and when RMDs, Social Security, or business income push your bracket back up.

If your current bracket is lower than you expect your bracket to be in retirement, converting now locks in the lower rate. If your bracket is the same or higher, the math tips against conversion. The framework below helps you figure out which scenario you're in.

How conversions are taxed

A Roth conversion is treated as ordinary income in the year you convert. The converted amount is added to your taxable income and taxed at your marginal rate — there's no special capital-gains treatment, no averaging, no exemption.

If you convert $60,000 from a traditional IRA and your other taxable income is $80,000 MFJ, your total taxable income for that year is $140,000. The $60,000 conversion stacks on top of your other income and is taxed starting at the marginal rate that applies at $80,000 — the 22% bracket in 2026.

You pay the tax now, from outside the IRA if possible (using savings or a taxable account). If you pay the conversion tax by withholding from the converted amount itself, you're effectively converting less money to Roth and may owe a 10% early-withdrawal penalty on the withheld amount if you're under 59½.

2026 tax brackets (taxable income after deductions)

These are the income ranges at which each marginal rate applies to your taxable income — that is, your income after subtracting the standard deduction ($32,200 MFJ / $16,100 single in 2026) or itemized deductions.¹

Bracket targeting: how much to convert each year

The most common Roth conversion strategy is to convert just enough each year to fill the current bracket without spilling into the next. Two common targets:

• Fill the 12% bracket: Convert up to $100,800 (MFJ) or $50,400 (single) in taxable income. If your other taxable income is $60,000 MFJ, you can convert up to $40,800 at 12%. This is a strong threshold because 12% federal is historically low — the 22% bracket starts immediately above it, and future RMDs or Social Security income may push you there regardless.
• Fill the 22% bracket: Convert up to $211,400 (MFJ) or $105,700 (single) in taxable income. For someone who expects to be in the 24–32% bracket in retirement, converting at 22% is compelling. The 8–10 percentage point spread between "pay now at 22%" and "pay later at 32%" is often the strongest economic argument for conversion.

Converting above the 22% bracket — into 24%, 32%, or 35% — is usually justified only in specific circumstances: extreme RMD projections, very long time horizons, estate-planning goals, or a known future high-income event (a business sale, for example).

Conversion tax calculator (2026 rates)

Enter your estimated taxable income before the conversion — that is, your wages, pensions, Social Security, capital gains, and other taxable income minus your standard or itemized deductions, but not including the conversion itself. The calculator will show the federal tax cost for different conversion amounts at 2026 marginal rates.

Calculator uses 2026 federal brackets per IRS Rev. Proc. 2025-32. Does not model IRMAA surcharges, AMT, Social Security taxation phaseout, or state-specific Roth exclusions. Use for directional planning only.

The IRMAA cliff: a hidden $2,000+ Medicare penalty

For people who are Medicare-eligible (age 65+) or approaching it, the Roth conversion tax bill isn't the only risk. The IRS reports your income to Medicare each year. If your modified adjusted gross income (MAGI) — which includes the conversion amount — crosses an IRMAA tier, your Part B and Part D premiums increase for the following two years.²

In 2026, the first IRMAA tier triggers at:

• $109,000 MAGI for single filers and married filing separately
• $218,000 MAGI for married filing jointly

Crossing the first tier adds approximately $81.20/month ($975/year) to your Part B premium and a corresponding Part D surcharge — per person, not per household. A couple both on Medicare who inadvertently crosses the joint threshold pays ~$1,950/year in surcharges on top of the regular premiums. Higher tiers add surcharges of $202.70/month, $324.30/month, and up to $487.00/month per person.

The critical quirk: IRMAA is based on your income two years prior. A 2026 conversion shows up in your 2028 Medicare premiums. This two-year lag means a large conversion can haunt your premiums long after the year you did it — but it also means you can appeal using a life-changing event form (SSA-44) if your income has since dropped.

The two 5-year Roth rules (they work differently)

Roth accounts have two distinct 5-year clocks, and confusing them can result in an unexpected tax bill or penalty.

Rule 1: The account 5-year rule (for tax-free earnings)

To withdraw Roth earnings tax-free, two conditions must both be met: (1) you are at least 59½, and (2) your Roth IRA has been open for at least 5 tax years. The 5-year clock starts on January 1 of the year you made your first Roth IRA contribution — to any Roth IRA, not necessarily the one you're drawing from. If you open your first Roth in 2026, the account satisfies the 5-year rule on January 1, 2031.

Good news: this clock is typically not an issue for 401(k) rollovers. If you're converting at age 55+ and won't touch Roth earnings until 59½, the account will usually be 5+ years old by then. But it matters if you open your first Roth IRA late in life — a 60-year-old who converts for the first time in 2026 cannot withdraw earnings tax-free until 2031, even though they're already past 59½.

Rule 2: The conversion 5-year rule (for penalty-free access to converted principal under 59½)

This rule affects people under 59½ who convert and want to access the converted principal before reaching that age. Unlike regular Roth contributions — which can be withdrawn at any time without tax or penalty — each Roth conversion has its own 5-year holding requirement before the converted principal can be withdrawn penalty-free.

If you're 54 and convert $100,000 in 2026, you cannot withdraw that $100,000 penalty-free until January 1, 2031, even though you'll be 59 by then. The good news: once you turn 59½, the conversion 5-year rule becomes irrelevant. You can withdraw Roth principal at any time without penalty after 59½ — assuming the account 5-year rule is also satisfied.

The conversion 5-year rule is mainly relevant for the Roth conversion ladder strategy — where someone retires early and pre-funds Roth accounts 5+ years in advance to create penalty-free income. If you retire at 50 and want Roth income at 55, you'd start converting in 2025 so the funds are accessible by 2030.

RMD reduction: the long-term case for converting now

Under SECURE 2.0 (enacted December 2022), RMD age is 73 for those born between 1951 and 1959, and 75 for those born 1960 or later.³ Roth IRAs have no RMDs during the owner's lifetime. That means every dollar in a Roth IRA is never subject to a mandatory distribution that forces income recognition and potentially pushes you into a higher bracket or an IRMAA tier you didn't expect.

For someone currently 58 with a $1.2M IRA and no Roth: at age 75, their RMD on a $2.4M IRA (assuming 4% real growth) would be approximately $2,400,000 ÷ 22.9 (Uniform Lifetime Table divisor at 75) = $104,803/year, stacked on top of Social Security. That could push them well into the 22% or 24% bracket — or trigger IRMAA — regardless of what they'd prefer.

Converting $60,000/year from 58 to 72 (14 years) at 22% federal would reduce that IRA by ~$840,000, cutting the RMD by roughly $36,700/year. The conversions would cost ~$13,200/year in federal tax. Whether that trade is worth it depends on your current vs. projected bracket, time horizon, estate plans, and state tax rules — but the math often favors it for people with substantial pre-tax balances and lower current income.

When conversion is the wrong call

A Roth conversion makes sense when you're paying tax at a lower rate now than you'd pay in retirement. It's the wrong move when:

• Your current bracket is already higher than your projected retirement bracket. If you're in peak earning years at 35% and expect to draw $80,000/year in retirement (12–22% bracket), deferring is almost certainly better.
• You'd need to pay the conversion tax from IRA funds. If you have to withhold tax from the conversion itself, you're effectively converting less money to Roth while also possibly incurring a 10% penalty on the withheld amount (if under 59½). The math only works cleanly when you pay the tax from after-tax savings.
• You're crossing a steep IRMAA tier. As discussed above, the Medicare surcharge can turn a 22% conversion into an effective 28%+ cost when you factor in the two-year premium impact.
• Your state taxes conversions heavily. A few states (like California, New York, New Jersey) offer no Roth conversion break — ordinary income rates apply. An 8–10% state tax on top of 22–24% federal makes the break-even harder to achieve, especially if you plan to move to a no-income-tax state in retirement.
• You have large charitable giving plans. A large traditional IRA is an excellent asset to leave to charity via a qualified charitable distribution (QCD — up to $111,000/year in 2026⁴) or to a charitable remainder trust. Heirs who are charity get pre-tax IRA dollars tax-free; converting to Roth just to leave to charity often accelerates tax unnecessarily.

A worked example: partial conversion over 10 years

Rachel, 56, just retired and rolled her $900,000 401(k) into a traditional IRA. Her only other income is a $48,000/year pension. She files single. Her taxable income before the pension is about $31,900 (after standard deduction of $16,100). Adding the pension: taxable income ≈ $31,900.

She's in the 12% bracket on most of her income. The top of the 12% bracket for single filers is $50,400 (taxable income). She has $50,400 − $31,900 = $18,500 of headroom before entering the 22% bracket. She also watches the IRMAA threshold: her MAGI (gross pension $48,000 + no other gross income) is $48,000 — well below the $109,000 single threshold. She can convert up to ~$61,000 before hitting the IRMAA cliff ($109,000 − $48,000 = $61,000).

Strategy: convert $18,500/year to fill the 12% bracket, and optionally layer in another $30,000/year at 22% if she decides the rate arbitrage is worth it. Over 10 years, $18,500/year × 10 = $185,000 converted at 12%, costing about $22,200 in federal tax (plus state). Her IRA shrinks from $900,000 to roughly $715,000 pre-RMD, and her Roth account grows tax-free. By the time RMDs kick in at 75, her RMD is materially lower.

Whether the additional $30,000/year at 22% makes sense depends on her estate plans, state tax, and Social Security income — all variables an advisor models with her specific numbers.

1. IRS Rev. Proc. 2025-32 — 2026 inflation-adjusted tax parameters including bracket thresholds (10%–37%) and standard deductions ($32,200 MFJ / $16,100 single). Values verified April 2026.
2. SSA POMS HI 01101.020 — IRMAA Sliding Scale Tables — 2026 IRMAA income thresholds: first tier at $109,000 (single) / $218,000 (MFJ). Part B surcharges: $81.20–$487.00/month above base premium of $202.90. Updated December 2025.
3. SECURE 2.0 Act of 2022 (Div. T of Consolidated Appropriations Act, 2023) — § 107 raised RMD age to 73 for individuals born 1951–1959, and 75 for those born 1960 or later. § 325 eliminated Roth designated account (Roth 401(k)/403(b)/TSP) lifetime RMDs starting 2024.
4. IRS 2026 Inflation Adjustments — QCD annual limit for 2026: $111,000 (inflation-adjusted from original $100,000 SECURE 1.0 limit). Roth IRA contribution income phaseout: $150,000–$165,000 single, $236,000–$246,000 MFJ. Values verified April 2026.

Tax values verified as of April 2026 against IRS Rev. Proc. 2025-32, SSA POMS, and CMS.gov.

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