The Roth Conversion Golden Window

Between retirement and Required Minimum Distributions lies a window — often 10 to 15 years — when your taxable income is lower than it will ever be again. This window is the optimal time for Roth conversions. This guide explains exactly how the window works, how IRMAA shapes your annual limit, and how to calculate your own runway year by year.

Why a window exists at all

For most high-earners, three income streams dominate their 50s: wages, retirement account growth (untouched), and investment income. In early retirement, those streams shift dramatically at once:

• Wages stop. Earned income drops to zero or near-zero at retirement.
• Social Security is often deferred. Filing at 70 rather than 62 increases lifetime benefits by roughly 8%/year. Retirees who delay spend several years with no SS income at all.
• RMDs haven't started. Traditional IRA and 401(k) balances compound without forced distributions — until age 73 (or 75 for those born in 1960 or later, per SECURE 2.0).⁵

This income trough — earned income gone, SS not yet claimed, RMDs not yet forced — puts many retirees in the lowest federal tax bracket they've seen since their 20s. That's the golden window.

The window has three phases

Not all years within the window are equal. The conversion opportunity changes substantially as you move through it.

Phase 1: Early retirement (roughly age 60–65)

This is often the widest phase. Medicare hasn't started — IRMAA doesn't exist as a constraint yet. Social Security is likely not running. Earned income is minimal. For a couple with modest other income, the bracket headroom for conversions can be enormous.

Example — couple, both 62, $60K of ordinary income (interest, dividends, part-time work), MFJ:

• 2026 standard deduction (MFJ): $32,200¹
• Taxable income before conversion: $60,000 − $32,200 = $27,800
• 22% bracket top (MFJ, taxable income): $201,050²
• Maximum conversion to stay within the 22% bracket top: $201,050 − $27,800 = $173,250/year

At this phase, the practical constraint is usually not the bracket — it's whether the couple has enough after-tax assets to pay the conversion tax without touching the IRA itself (the optimal approach), and whether large early conversions make NPV sense given their specific rate differential and legacy goals.

Phase 2: Medicare years (age 65–72 or 74)

Once Medicare starts, IRMAA becomes the dominant constraint on annual conversion size. Medicare Part B and D premiums surcharge above income thresholds, based on your MAGI from two years prior. Roth conversion income adds directly to MAGI.

Important: the two-year IRMAA lookback means large conversions at 63 affect your Medicare premiums at 65. Planning the window requires projecting forward, not just optimizing the current year in isolation.

The 2026 IRMAA tier 1 threshold (MFJ): $218,000 MAGI.³ Most conversion plans target staying under this first tier unless deliberately crossing it is worth the NPV tradeoff.

Using the same couple from Phase 1, now with Medicare running and the same $60K baseline income:

• IRMAA Tier 1 MAGI threshold (MFJ): $218,000
• Baseline MAGI (no conversion): $60,000
• Maximum conversion before Tier 1 surcharge: $218,000 − $60,000 = $158,000/year

The window narrowed by $15K/year relative to Phase 1 — not because of the bracket, but because of IRMAA. For a couple converting over 10 years, that's $150K less converted by staying IRMAA-clean. Whether staying clean is the right call depends on how much each IRMAA tier costs relative to the lifetime benefit of additional conversion.

Social Security adds a further complication once it starts: up to 85% of SS benefits become taxable ordinary income once combined income exceeds $44,000 MFJ.⁴ Conversion income stacks on top, so a couple receiving $50,000/yr of SS may find $42,500 of it folded into their MAGI calculation — compressing conversion headroom further.

Phase 3: Final years before RMDs

In the last one to three years before RMDs begin, the window is closing and the stakes per year are highest. Most of the low-hanging conversion opportunity has either been captured in earlier years — or not. A specialist typically targets the exact MAGI level that fills remaining bracket headroom without tripping IRMAA or the next SS taxation cliff.

This is also the phase where legacy planning comes into focus: Roth accounts pass to heirs income-tax-free and have no lifetime RMD requirement. Traditional balances left unconverted will be distributed by heirs as ordinary income over 10 years (the SECURE Act inherited-IRA rule). For a $1M unconverted balance, the difference can be $200-300K of tax burden shifted to heirs.

Why the 1960+ cohort has a longer runway

The SECURE 2.0 Act (§ 107) extended the RMD start age to 75 for anyone born January 1, 1960 or later — two years later than the prior 73-year-old start age.⁵ This is a meaningful structural advantage:

• Someone born in 1961, retiring at 62, now has a 13-year window instead of 11 years.
• At $150K/year of conversions, two extra years = $300K more converted at the favorable rate — $30–50K of additional lifetime tax savings from the rate differential alone.
• The longer window also reduces annual conversion urgency, providing more flexibility to manage cash flow and IRMAA exposure year by year rather than racing to convert.

If you were born before 1960, your RMD start age is 73. Check your specific birth year against the IRS table — the SECURE 2.0 rules are based on the year you reach each age, not just a simple birth-year cutoff.

What a year-by-year calculation looks like

Every year within the window requires a fresh calculation. The inputs that shift annually:

1. Other ordinary income — interest, short-term gains, pension distributions, taxable Social Security amount, any part-time work.
2. MAGI for IRMAA lookback — this year's conversion affects Medicare premiums two years from now. Building a forward model across the full window is essential.
3. Bracket boundaries — tax brackets adjust for inflation each year (IRS releases new brackets in October). Running the same conversion dollar amount year over year without recalculating gradually drifts toward over-converting.
4. State residency — 9 states have no income tax; others (CA, NY, MN) apply graduated rates that can make large single-year conversions materially more expensive. A planned move to a no-tax state is a reason to delay conversion until after the move.

The annual calculation framework:

1. Estimate all ordinary income for the year (SS taxable portion, interest, pension, RMDs if any).
2. Subtract the standard deduction (plus any 65+ supplemental deduction) to get taxable income before conversion.
3. Identify bracket headroom: (bracket top you're targeting) minus (taxable income before conversion).
4. Identify IRMAA headroom: (IRMAA tier threshold you're targeting) minus (MAGI before conversion).
5. Convert the lower of the two limits — unless a deliberate IRMAA crossing is worth the math.
6. Execute by December 31. Roth conversions cannot be extended past year-end.

Front-loading vs. spreading conversions

Two frameworks emerge in window planning:

Spread conversions steadily. Convert a consistent annual amount — enough to fill the target bracket without IRMAA exposure. Works well when the rate differential is consistent, the window is long, and the couple wants predictable annual tax bills. Lower risk of rate-change regret.

Front-load Phase 1 before Medicare. Convert more aggressively in early retirement when IRMAA doesn't apply, potentially going deeper into the 24% bracket. Pays slightly higher marginal rate now to avoid the combined bracket-plus-IRMAA constraint in Phase 2. Requires enough after-tax assets to pay conversion taxes without dipping into the IRA.

The right answer depends on state tax, SS timing, health, cash-flow needs, and the NPV of compounding across different scenarios. There is no universal rule — which is the whole point of building a multi-year model with a specialist.

What happens when the window closes

RMDs don't end Roth conversion opportunity — you can still convert after they begin — but they fundamentally reshape the math:

1. RMD income fills your bracket first. You can't replace an RMD with a conversion; you must take the RMD and then convert on top of it. For a $3M IRA, the first-year RMD at 73 is approximately $3,000,000 ÷ 26.5 (IRS Uniform Lifetime Table divisor) ≈ $113,000 of forced ordinary income. Adding Social Security and other income, bracket headroom for voluntary conversion often disappears entirely.
2. The urgency flips. Inside the window, conversions are proactive — getting ahead of forced distributions. After RMDs start, every dollar of conversion is reactive, and the math typically (not always) weakens.