Complete Roth Conversion Strategy Guide

Roth conversions done well are often the single most valuable financial move of a retiree's life. Done poorly, they burn tax needlessly. The difference is multi-year planning against bracket boundaries, IRMAA thresholds, and legacy goals.

Why conversions work

A traditional IRA is like a partnership with the government: they own the taxes on all future growth + principal. Convert to Roth and you pay the government's share now — ending the partnership. The math wins when:

• Your current tax bracket is meaningfully lower than your future tax bracket (RMD era, or from bracket increases in law).
• You have years of growth ahead of the Roth balance (compounding tax-free beats compounding tax-deferred).
• You're leaving money to heirs (inherited Roth = 10 years of tax-free growth + tax-free distributions vs. inherited traditional with ordinary-income tax on distributions).

The 60-73 golden window

For most retirees, this is when the math tilts strongly toward conversion:

• Age 60-65: Retired or semi-retired. Earned income dropped. Social Security not yet claimed (if delayed to 70). Lowest bracket of your life since your 20s.
• Age 65-70: Medicare starts; IRMAA becomes a factor. SS may start at 67. Window narrows.
• Age 70-72: SS is on. Pre-RMD but narrowing window. Last chance before RMDs kick in at 73.
• Age 73+: RMDs add mandatory income. Still possible to convert but your bracket is usually higher. Math weakens.

Bracket filling precision

The goal isn't to convert your whole balance in one year — that pushes you into the 32%+ bracket, negating the benefit. It's to convert just enough annually to fill your current (low) bracket without crossing into the next.

2026 federal brackets (MFJ, per IRS Rev. Proc. 2025-32):¹

• 10% bracket: $0 – $23,200
• 12% bracket: $23,201 – $94,300
• 22% bracket: $94,301 – $201,050
• 24% bracket: $201,051 – $383,900
• 32% bracket: $383,901 – $487,450
• 35% bracket: $487,451 – $768,600
• 37% bracket: $768,601+

For a couple with $60K of non-conversion income, converting $141K tops off the 22% bracket precisely ($201,050 − $60,000 = $141,050 of conversion headroom). Annual re-calibration matters — each year your other income shifts.

IRMAA — the hidden cliff

Medicare Part B + D premiums surcharge above income thresholds. Two-year lookback: 2026 premiums are based on your 2024 MAGI. 2026 tiers (single filer; MFJ thresholds are 2×):²

• Tier 1: $109,000+ MAGI → +$81.20/mo Part B + $14.50/mo Part D
• Tier 2: $137,000+ → +$202.90/mo Part B + $37.40/mo Part D
• Tier 3: $171,000+ → +$324.64/mo Part B + $60.30/mo Part D
• Tier 4: $205,000+ → +$446.38/mo Part B + $83.10/mo Part D
• Tier 5: $500,000+ → +$487.00/mo Part B + $91.00/mo Part D

Base Part B premium in 2026: $202.90/month. MFJ thresholds are 2× the single-filer thresholds, topping out at $750,000. A conversion that bumps you into a higher tier adds $1,100-6,900/yr of Medicare premiums per person — an unexpected effective tax increase. Specialists keep conversions just below threshold edges, and appeal via Form SSA-44 when a life-event MAGI change (retirement, loss of income) is otherwise misrepresenting current ability to pay.³

5-year rule

Each Roth conversion has its own 5-year clock before the converted amount can be withdrawn penalty-free (if you're under 59½).⁴ Separate from the 5-year rule on Roth IRA contributions (which applies to earnings). For retirees 59½+ already, the 5-year conversion clock doesn't apply to withdrawals of converted funds — only the first-contribution 5-year clock applies to earnings. Still affects inherited Roth dynamics.

Pro-rata rule

If you have multiple traditional IRAs including ones with after-tax basis (backdoor Roth contributions, non-deductible contributions), the pro-rata rule treats all IRAs as a single pool for conversion purposes.⁵ You can't cherry-pick "just the after-tax portion" to convert. Track basis on Form 8606 annually. For those with meaningful basis: consider rolling pre-tax IRA balance into a 401(k) (which accepts incoming rollovers) to isolate the after-tax remainder in IRA, then convert cleanly. SEP and SIMPLE IRAs count toward the pro-rata pool; inherited IRAs do NOT.

Common mistakes

• Big one-year conversion. Pushes you into a high bracket. Multi-year ladder is almost always better.
• Ignoring IRMAA. The surcharge adds 1-3% to the effective cost of conversion.
• Converting in a high-state-tax year before moving to no-state-tax state. Time conversions after moving to FL/TX/WA etc. for meaningful state-tax savings.
• Converting too little. Most retirees err conservative. If bracket differential supports it, fuller conversion accelerates the benefit.
• Not tracking basis. Form 8606 each year with non-deductible contributions or post-tax rollovers. Lost basis = double taxation at withdrawal.

Sources

1. Tax Foundation — 2026 Federal Tax Brackets (per IRS Rev. Proc. 2025-32).
2. Kiplinger — 2026 Medicare IRMAA Brackets. Base Part B: $202.90/month.
3. SSA Form SSA-44 — IRMAA Life-Changing Event Appeal.
4. IRC § 408A(d)(2) and (3) — Roth IRA Distribution Ordering Rules and 5-Year Rules.
5. IRS Form 8606 — Nondeductible IRAs. Pro-rata rule under IRC § 408(d)(2).
6. IRS — IRA Contribution Limits (2026 Roth contribution limit: $7,500).

Brackets, limits, and IRMAA thresholds verified against IRS and SSA publications as of April 2026. Confirm your specific situation with a specialist.