Retiring at 61 With $1.9 Million in a 401(k)? Four Years Left to Convert Before Medicare Starts Counting Your Income

Walking away from a paycheck at 61 with $1.9 million in a 401(k) creates a narrow, high-value window that most early retirees waste. You have four calendar years before Medicare enrollment at 65, but only two of those years are truly “free” for Roth conversions. After that, every extra dollar of income you generate starts driving up the Medicare premiums you will pay for the rest of your life.

The mechanic is the IRMAA two-year lookback, and it is the single most expensive rule in retirement most people never plan for.

Why Age 63 Is the Real Medicare Deadline

Medicare uses your modified adjusted gross income from two years prior to set your Part B and Part D premiums. If you turn 65 in 2030, your first-year Medicare premiums are based on your 2028 tax return. That means income in the year you turn 63, and every year after, follows you into Medicare.

For a 61-year-old retiring today, that leaves 2026 and 2027 as the only years to run large Roth conversions without any Medicare consequence. Conversions in 2028 and beyond will land on a Social Security statement showing a higher premium, and the surcharge is set annually based on that lookback year.

The premiums are not trivial. The standard 2026 Part B premium is $202.90 per month per person. A married couple filing jointly with MAGI above $218,000 pays an extra $81.20 each on Part B plus $14.50 each on Part D. Higher tiers escalate quickly, and at the top of the scale a couple above $750,000 pays $689.90 per month each for Part B alone. IRMAA works as a cliff, not a slope — one dollar over a threshold pulls in the full surcharge.

What a Conversion Actually Costs in 2026

Assume a married couple, both 61, retiring now with no wages. Under the 2026 brackets, the 24% rate starts at $211,400 of taxable income for joint filers, and the standard deduction is $32,200. That means they can convert roughly $243,000 from the 401(k) and stop the last dollar right at the top of the 22% bracket.

The tax bill on that conversion runs a blended rate in the mid-teens, because the first $24,800 fills the 10% bracket, the next chunk fills 12%, and only income above $100,800 hits 22%. Doing the same conversion in the same couple’s 70s, on top of Social Security and RMDs, would push most of it into the 24% or 32% brackets. Paying 15% to 18% now to avoid 24% to 32% later is the entire game.

Run that playbook in 2026 and 2027 and you can move nearly $500,000 out of pre-tax and into a Roth before IRMAA even starts watching. Every dollar converted also permanently shrinks the RMDs that begin at 75. Those quiet years between your last paycheck and your first required withdrawal are the cheapest tax rate you may ever see again, which is the whole subject of our free Roth Window guide.

Where to Park the Tax Money

Conversions require cash to pay the IRS, and pulling that cash from the 401(k) itself defeats the purpose. A short Treasury ladder is the cleanest source. The 10-year Treasury yield sits near 4.7%, and shorter maturities are yielding in the same neighborhood, so setting aside two years of conversion taxes in Treasuries earns real interest while you wait.

Social Security planning stacks on top of this. The 2027 COLA is tracking near 3.1%, and delaying benefits to 70 continues to be the highest-return “bond” available to a healthy 61-year-old. Delaying also keeps your provisional income low during the conversion window, which keeps more of the 12% and 22% brackets available for Roth conversions.

Three Moves to Make Before December 31

1. Model a two-year conversion ladder for 2026 and 2027. Fill the 22% bracket both years. Confirm the 2028 conversion stays under the $218,000 joint IRMAA threshold, because 2028 income sets your first Medicare premium.
2. Move two years of conversion taxes into Treasuries now. With the 10-year near 4.7% and shorter maturities close behind, a laddered T-bill position covers April tax bills without touching the 401(k).
3. Decide on Social Security timing before you start converting. Claiming at 62 while converting at the 22% bracket often pushes 85% of the benefit into taxable territory and negates the savings. Delaying past 65 keeps the conversion window clean.

The four-year gap between retirement and Medicare looks generous until you realize the IRMAA clock starts ticking at 63. Use the first two years hard, or pay the surcharge for the rest of your life.

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