Post-Sale Roth Conversion: $500K Low-Income Year Ladder

The year a founder sells the business is the highest-income year of their life. The year that follows is often the lowest. AGI may drop from $25 million in the sale year to $200,000 the following year as the W-2 stops, the capital gain is fully recognized in the prior year, and the new portfolio is still ramping into dividend and interest production. This income trough is the most valuable tax-planning window of the founder's lifetime — and most founders miss it.

The 12, 22, and 24 percent federal brackets are wide open. Traditional IRA and Traditional 401(k) balances that will eventually come out at 32-37 percent (after RMDs, Social Security, IRMAA, and post-sale portfolio income compound) can be converted to Roth at the lower current rate. A $500K conversion at 24 percent costs $120K of federal tax now and avoids $185K of federal tax later — net saving of $65K. Stacked across 3-5 low-income years, the cumulative benefit reaches $300K-$500K.

The mechanics involve four moving parts: the pro-rata rule under IRC sec. 408(d)(2), the 5-year conversion clock under sec. 408A(d)(2)(B), the IRMAA cliffs at $103K and $206K MAGI, and the SECURE 2.0 RMD age at 73 or 75. Sequence and sizing matter.

The post-sale income trough: typical magnitude

A typical pre-to-post-sale income trajectory for a founder of a successful business:

• 5 years before sale: W-2 $400K + business pass-through $1.5M = $1.9M AGI
• 2 years before sale: W-2 $500K + business pass-through $2M = $2.5M AGI
• Sale year: W-2 $500K + capital gain $20M = $20.5M AGI
• Year +1: portfolio dividends + interest = $150K-$300K AGI
• Year +2: same level + modest capital gains realized = $200K-$400K AGI
• Year +3 through age 64: $200K-$500K AGI as portfolio grows
• Age 65: Medicare begins; IRMAA from year +3 MAGI controls
• Age 70: Social Security begins (if delayed); AGI rises by ~$48K
• Age 73-75: RMDs begin; AGI rises by 4-5% of pre-tax balance annually

The 3-7 year window between sale closing and RMD onset is the conversion ladder zone. For founders aged 55-60 at sale, the window stretches 13-20 years; for founders aged 65-68, the window is 5-10 years.

The mechanics: bracket-filling math

A Roth conversion takes pre-tax dollars from a Traditional IRA or Traditional 401(k), pays ordinary income tax on the conversion amount, and moves the after-tax amount into a Roth IRA. The Roth IRA then grows tax-free, future qualified withdrawals are tax-free, and the Roth has no RMD requirement.

The conversion is taxed at the founder's marginal bracket in the year of conversion. To make the conversion worthwhile, the current bracket must be lower than the eventual withdrawal bracket. For most post-sale founders, the comparison is:

• Current bracket (post-sale low-income year): 22-24% federal
• Eventual withdrawal bracket (RMD year + SS + portfolio income): 32-37% federal
• Net savings: 8-15 percentage points per converted dollar

The 2026 federal brackets (MFJ):

• 12% bracket: $23,851 - $96,950
• 22% bracket: $96,951 - $206,700
• 24% bracket: $206,701 - $394,600
• 32% bracket: $394,601 - $501,050
• 35% bracket: $501,051 - $751,600
• 37% bracket: $751,601+

For a founder with $150K of base AGI and a $250K Roth conversion target, the conversion fills the 22% bracket to $206,700 ($56,700 at 22% = $12,474) and continues into the 24% bracket ($193,300 at 24% = $46,392). Federal tax on the $250K conversion: ~$58,866 (effective rate 23.5%). Compared to eventual withdrawal at 37%: $250K × 37% = $92,500. Savings: $33,634.

The pro-rata rule under IRC sec. 408(d)(2)

IRC sec. 408(d)(2) requires that pre-tax and after-tax IRA dollars be treated pro-rata in any distribution or conversion. The rule applies at the aggregate level across all Traditional, SEP, and SIMPLE IRAs (NOT 401(k) plans).

For founders who have made nondeductible contributions to Traditional IRA (or who have done partial Roth conversions previously and left the basis in), the pro-rata blending complicates the conversion math:

Example: founder has $2M of Traditional IRA balance, of which $50K is after-tax basis (from past nondeductible contributions). The after-tax proportion is 2.5 percent. A $500K conversion is:

• Taxable portion: $487,500 (97.5%)
• Tax-free return of basis: $12,500 (2.5%)
• Remaining Traditional IRA balance: $1.5M with $37,500 of remaining after-tax basis

The strategies to work around pro-rata:

• Roll Traditional IRA into 401(k). Most employer 401(k) plans accept direct rollovers from IRAs. Sec. 408(d)(2) does NOT apply to 401(k) plans. By rolling pre-tax Traditional IRA balances into a 401(k), the after-tax basis is isolated in the (smaller) remaining Traditional IRA and can be converted tax-free.
• Solo 401(k) for self-employed. Founders with any self-employment income can establish a Solo 401(k) and roll Traditional IRAs into it.
• Time the conversion. The pro-rata test is done at year-end (December 31), not at the conversion date. A December 30 rollover into a 401(k) eliminates the IRA balance from the year's pro-rata math.
• Mega backdoor Roth. For founders with after-tax 401(k) contributions, the conversion of after-tax 401(k) balance to Roth follows different rules than the pro-rata IRA rule.

The 5-year conversion clock under sec. 408A(d)(2)(B)

Each Roth conversion starts its own 5-year clock for the converted principal. The clock determines when the converted amount can be withdrawn without the 10 percent early-withdrawal penalty:

• Before age 59 1/2 AND less than 5 years from conversion: 10% penalty applies to withdrawal of converted principal
• Before age 59 1/2 BUT 5+ years from conversion: no penalty
• After age 59 1/2: no penalty regardless of conversion timing

For a 55-year-old post-sale founder considering an aggressive conversion ladder, the 5-year rule constrains early access:

• Convert $500K at age 55: penalty-free withdrawal of principal at age 60 (the later of 5 years or age 59 1/2)
• Convert $500K at age 57: penalty-free withdrawal at age 62
• Convert $500K at age 60: penalty-free withdrawal immediately (over 59 1/2)

For founders who do not need to access the converted principal before age 59 1/2 (typical for $20M+ exits where cash from the sale funds living expenses), the 5-year clock is not binding. For founders 50-59 with limited liquidity, the conversion amount should be sized to what they will not need in the next 5 years.

IRMAA cliffs for Medicare-eligible converters

Medicare Part B and Part D premium surcharges (IRMAA) kick in based on MAGI from two years prior. For a 2026 Medicare beneficiary, 2024 MAGI controls the surcharge. The cliffs are unforgiving — crossing the threshold by $1 triggers the full higher tier.

2026 IRMAA tiers (MFJ MAGI):

• ≤ $206K: base Part B premium $185/mo, no surcharge
• $206K - $258K: +$74/mo each (~$1,776/yr total for couple)
• $258K - $322K: +$185/mo each (~$4,440/yr)
• $322K - $386K: +$295/mo each (~$7,080/yr)
• $386K - $750K: +$406/mo each (~$9,744/yr)
• $750K+: +$444/mo each (~$10,656/yr)

For a 65-plus founder, a $500K conversion that pushes MAGI from $200K to $700K creates a two-year IRMAA penalty of approximately $9,744/year × 2 years = $19,488 of additional Medicare premium.

The IRMAA cost compresses but does not eliminate the conversion benefit. On a $500K conversion saving $65K of long-term tax (24% now vs. 37% later), the IRMAA hit is roughly $19,500 — net savings still positive at ~$45,500. But the math compresses; for founders right at the IRMAA cliff, smaller conversions that stay just under the threshold may be more efficient.

For founders under 65 (pre-Medicare), IRMAA does not yet apply — the optimal converson window is age 55-64 (or 55-63 to avoid the year-before-65 IRMAA lookback).

Worked example: $2M Traditional balance, 60-year-old post-sale founder

Patricia sold her medical-device company in 2025 for $18M. She is 60, lives in Florida (no state tax), and has $2M in a Traditional IRA + 401(k) balance (rolled to IRA after the sale). She plans to take Social Security at 70 ($48K/year) and faces RMDs starting at age 75 (born 1965).

Post-sale AGI baseline: $200K (portfolio dividends, interest, small capital gains). She has 13 years of low-income window before RMDs begin.

Ladder plan: convert $300K per year for 7 years (2026-2032)

Total converted: $1,950,000 over 7 years. Total federal tax paid: ~$470,600 (effective rate 24.1%).

Critique: the ladder pushes Patricia into the 32% bracket each year. Conversions partially fill the 32% bracket above $394,600 MFJ. The effective rate on the marginal $300K of conversion is around 28-29% — better than the 37% she would face at age 75+ but not as good as filling the 24% bracket only.

Alternative ladder: convert $200K per year for 9 years

Smaller annual conversions keep Patricia in the 24% bracket:

• Year 1 (age 60): Base $200K + Convert $200K = $400K AGI. Top bracket: 24% ($206K-$395K). Federal tax on conversion: $48K
• Year 2: same math, $200K converted, $48K tax
• ...continuing 9 years
• Total converted: $1.8M, total tax: ~$432K (effective rate 24%)

Smaller ladder: less converted in absolute terms ($1.8M vs $1.95M) but at a lower effective rate (24% vs 24.1%). Marginal difference is small in this case because Patricia's base AGI is already at the 24% boundary. For lower-base-AGI founders, the smaller-ladder strategy is materially better.

Future RMD savings

Without conversions, Patricia's $2M Traditional balance grows at 5 percent real return to about $3.4M by age 75. First-year RMD (divisor 25.5): $133K. Combined with SS ($48K) and portfolio income ($300K by then): $481K AGI in the 32% bracket.

With $1.95M converted by age 66: remaining Traditional balance grows at 5% from $50K (very small amount remaining) to about $76K by age 75. First-year RMD: $3K. Total AGI in 2041 (age 75): ~$340K. Top bracket: 32% (vs 32%) — but on a much smaller pre-tax balance.

Over the 25-year retirement horizon (age 75 to 100), the cumulative RMD reduction saves Patricia approximately $1.5M-$2M in cumulative federal tax. Net of the upfront $470K conversion tax, her family is approximately $1M-$1.5M better off — and her heirs inherit Roth dollars (tax-free 10-year drawdown under SECURE Act) instead of Traditional dollars (ordinary income to heirs).

Common mistakes

• Converting too little. Founders often convert $50K-$100K per year out of caution. The bracket-filling math rewards larger conversions (up to the 24% boundary). $50K/year leaves 80% of the bracket unused and the long-term tax savings is small.
• Converting too much in a single year. Pushing into 35-37% brackets defeats the purpose. The conversion rate should be at or below the expected future withdrawal rate.
• Ignoring the pro-rata rule. Founders with after-tax IRA basis (from past nondeductible contributions or backdoor Roths) may have unexpected pro-rata blending. Check Form 8606 history before converting.
• Triggering IRMAA cliffs. For 65+ founders, large conversions create two-year IRMAA penalties. Sizing the conversion to stay just under the IRMAA threshold can preserve $5K-$10K of annual Medicare costs.
• Skipping the low-income window. The post-sale years are non-repeating. Failing to convert during the trough means paying RMD-year tax rates later, which is often 13+ percentage points higher.
• Not coordinating with charitable giving. Charitable contributions reduce AGI. A founder with $200K of base AGI who plans a $300K Roth conversion AND a $100K DAF contribution effectively converts at lower brackets ($200K - $100K + $300K = $400K AGI). Careful sequencing maximizes the bracket arbitrage.

State-tax integration

State income tax on the conversion follows the founder's residence at the time of conversion. For founders in California (13.3%), New York (10.9%), or other high-tax states, the conversion tax is materially higher. For founders relocating to Florida, Texas, or Nevada in the post-sale window, executing the conversion AFTER the move saves the state-tax friction.

A founder who moves from California to Florida in 2026 and converts $300K in 2027 saves $39,900 of CA state tax (13.3% on $300K) versus converting before the move. Over a 7-year ladder, the cumulative state-tax savings can exceed $250K.

Key takeaways

• The year(s) after a business sale form a unique low-income window — typically the lowest-AGI years of the founder's life. Roth conversions during this window at the 22-24% bracket save 10-13 percentage points versus eventual RMD-year withdrawal at 32-37%.
• The pro-rata rule under IRC sec. 408(d)(2) blends pre-tax and after-tax IRA balances at the aggregate level. Rolling Traditional IRA balances into a 401(k) before converting isolates the after-tax basis and simplifies the conversion math.
• Each Roth conversion starts its own 5-year clock for penalty-free withdrawal of converted principal under sec. 408A(d)(2)(B). For founders 59 1/2+, the 5-year rule does not impose a penalty; for younger founders, the clock constrains liquidity access.
• IRMAA cliffs at $103K/$206K (and above) compress the conversion benefit for Medicare-eligible founders. Sizing conversions to stay just under the IRMAA threshold preserves Medicare premium savings.
• A typical ladder converts $200K-$500K per year for 5-9 years, drawing down the Traditional balance by $1.5M-$3M before RMDs begin. Cumulative federal-tax savings over a 25-year retirement horizon often reach $300K-$1.5M.
• State-tax considerations interact. A post-sale relocation to a no-tax state should be timed before the conversion ladder begins to maximize savings.