Multi-year Roth ladder + bracket arbitrage methodology

What bracket arbitrage means in Roth planning

Bracket arbitrage is the practice of converting just enough from a traditional IRA to Roth each year to fill your current tax bracket without crossing into the next one. The logic is that your marginal tax rate today is known and relatively controllable; your marginal rate in retirement is uncertain and likely to be higher if RMDs, Social Security, and other income stack in the same years.

A multi-year Roth ladder executes this systematically — converting a deliberate amount each year across a 5-to-15-year window before RMDs begin, before Social Security creates a higher effective marginal rate, and while the account balance is smaller and the bracket arithmetic is more favorable.

2026 OBBBA bracket structure and bracket-fill calculation

2026 Federal Tax Brackets — IRC §1 as amended by OBBBA (Pub. L. 119-XX):
(Indexed for inflation; apply to taxable income, not MAGI)

Single filers:
  10%   $0         – $11,925
  12%   $11,926    – $48,475
  22%   $48,476    – $103,350
  24%   $103,351   – $197,300
  32%   $197,301   – $250,525
  35%   $250,526   – $626,350
  37%   above $626,350

Married Filing Jointly (MFJ):
  10%   $0         – $23,850
  12%   $23,851    – $96,950
  22%   $96,951    – $206,700
  24%   $206,701   – $394,600
  32%   $394,601   – $501,050
  35%   $501,051   – $751,600
  37%   above $751,600

Bracket-Fill Conversion Formula:
  Target Bracket Ceiling (e.g., top of 22%): $103,350 (single)
  Existing Taxable Income (W-2, Schedule C, SS, etc.): $75,000
  Remaining 22% Bracket Headroom: $103,350 − $75,000 = $28,350
  Maximum Conversion Without Crossing into 24%: $28,350

  (Also check IRMAA Tier 1 MAGI threshold at $109,000 single —
  taxable income and MAGI diverge by deductions; verify both.)

The key discipline: taxable income and MAGI are not the same number. Taxable income is after the standard deduction or itemized deductions. IRMAA uses MAGI, which adds back certain items. A conversion that appears to stay in the 22% bracket on a taxable-income basis can still cross an IRMAA tier on a MAGI basis.

Multi-year ladder math

Multi-Year Roth Ladder — Compounding Math:

Assumptions (illustration only):
  Starting traditional IRA balance: $600,000
  Annual Roth conversion: $30,000/year
  Annual investment return: 6%
  Bracket: 22% on conversions (rate known and locked in each year)
  Years of conversion: 10 (ages 60–69, before RMDs at 75)

Year 1:
  Beginning balance: $600,000
  Conversion: $30,000 → moved to Roth, taxed at 22% = $6,600 paid
  Growth on remaining $570,000 at 6%: +$34,200
  End balance: $604,200 traditional, $30,000 in Roth

Year 10 (cumulative):
  Converted to Roth: $300,000 (at ~$66K total tax paid, avg. 22%)
  Roth balance grown at 6%: ~$395,000 (tax-free)
  Traditional IRA: reduced from $600K to ~$480K (still growing;
    future RMDs are smaller; future SS provisional income lower)

Net savings vs. no-conversion scenario:
  Depends on future marginal rate. If RMDs push future rate to 32%:
    Tax eventually paid on $300K at 32%: $96,000
    Tax paid via conversions at 22%: $66,000
    Gross savings: $30,000 + compounding on the Roth's tax-free growth

The illustration is deterministic. Real-world results depend on actual investment returns, future legislation, future tax rates, actual income in each year, and longevity. The calculator models the inputs as given; the strategic judgment about whether to execute belongs to the taxpayer and their CPA or financial planner.

Historical bracket context

The OBBBA of 2026 extended the Tax Cuts and Jobs Act (TCJA) bracket structure that was scheduled to sunset after 2025. Under pre-OBBBA law, the 37% top rate would have reverted to 39.6% and the 22% bracket ceiling would have dropped, pushing more ordinary income into higher brackets. The extension locked in relatively favorable rates for Roth conversion planning through the foreseeable future, but rates remain subject to future legislation.

Bracket arbitrage implicitly bets that current rates are favorable relative to future rates. That bet has been correct for pre-retirees in most historical scenarios, primarily because RMD stacking, Social Security inclusion, and reduced deductions in retirement tend to push effective marginal rates higher even without statutory bracket changes.

Edge cases

• Social Security tax cliff. For taxpayers already receiving Social Security, conversion income can trigger up to 85% of benefits becoming taxable (IRC §86). This creates an effective marginal rate well above the nominal bracket rate in the $25,000–$34,000 (single) / $32,000–$44,000 (MFJ) provisional income range. The bracket-fill formula must account for this implicit surtax on each conversion dollar.
• 0% long-term capital gains bracket. The 0% long-term capital gains rate applies to income within the 10% and 12% ordinary brackets (up to $48,350 single / $96,700 MFJ for 2026). A Roth conversion that fills the 12% bracket eliminates the 0% LTCG space for that year by pushing other income into a higher bracket. Taxpayers with substantial taxable-account gains should model the interaction before converting.
• Standard deduction leverage. The 2026 standard deduction ($15,000 single / $30,000 MFJ, indexed under OBBBA) reduces taxable income before the bracket applies. A single pre-retiree with no other income can convert up to $63,475 ($15,000 standard deduction + $48,475 top of 12% bracket) before hitting the 22% bracket — with zero federal tax on the first $15,000 of conversion due to the deduction.
• State tax treatment. Multi-year ladders work best in states with no income tax or states that exclude retirement income. In high-tax states (California 13.3% top rate; New York 10.9%), each conversion dollar carries a meaningfully higher blended tax cost that may alter the break-even timeline.
• Annual bracket indexing. Brackets are indexed for inflation annually per IRS Rev. Proc. issued each fall. Ladder models that project conversion amounts 10 years forward should build in a nominal bracket-width growth assumption (historically 2-3% annually) or the model will systematically overstate how much conversion headroom exists in future years.

Named-expert guidance

Sources

• IRC §1 — Tax imposed; 2026 bracket structure per OBBBA (Pub. L. 119-XX)
• IRS Rev. Proc. 2025-XX — Annual cost-of-living adjustment for income tax parameters (standard deduction, bracket thresholds, phase-out ranges)
• Pre-OBBBA bracket structure (TCJA sunset comparison reference) — IRS Rev. Proc. 2017-58 (TCJA rate structure) and the Tax Policy Center's TCJA sunset analysis for historical context
• IRS Publication 590-B — Distribution rules and Roth conversion mechanics