Retiring at 62 creates a rare 3-year window where a couple can shelter roughly $133,000 of gross income at just 12% before Social Security and RMDs begin.

Converting roughly $93,000 yearly to a Roth for three years moves $280,000 out of a 401(k) at the 12% rate, which helps them avoid the 22% to 24% rates that kick in once RMDs and Social Security stack together in their 70s.

Only age 62 is truly IRMAA-free. At 63 and 64, keeping MAGI under $218,000 is essential to avoid hundreds of extra dollars monthly in Medicare premiums due to the two-year lookback.

Read More: Avoid these 13 retirement mistakes before they derail your future (sponsor)

Picture a couple, both 62, who just handed in their notices. Their combined 401(k) balances sit near $1.6 million, they own their house, and Medicare is three birthdays away. Between now and age 65, they have the rarest thing in retirement planning: a window where they control almost every line on their tax return. Ed Slott made the same point in a recent Morningstar interview headlined Don't Waste Your Low-Tax Years in Retirement, and the math behind that warning is worth walking through in dollars.

The engine here is the 2026 tax code. A married couple filing jointly gets a standard deduction of $32,200, and the 12% bracket runs up to $100,800 of taxable income. Stack those together and roughly $133,000 of gross income can hit the 1040 while the top marginal rate stays at 12%. No paycheck is coming in. Social Security has not started. Required minimum distributions do not begin until age 73. The line labeled "taxable income" is essentially a dial the couple gets to set.

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That dial has a purpose. Every dollar left inside the traditional 401(k) is a future dollar of ordinary income that will eventually stack on top of Social Security and, later, RMDs. Moving money to a Roth now, at 10% or 12%, sidesteps a 22% or 24% withdrawal in the couple's 70s, plus the Social Security taxation cascade and IRMAA surcharges that come with it.

Assume the couple has $40,000 of dividends, interest, and a small pension. To fill the 12% bracket, they can convert about $93,000 from the 401(k) to a Roth IRA and land near the top of that $100,800 threshold. Federal tax on the conversion runs roughly $11,000, an effective rate near 12%. Repeat that for three years and about $280,000 of pretax money moves to a Roth, where it grows without RMDs and comes out tax-free.

Willing to pay 22%? The 24% bracket does not begin until $211,400 of taxable income for joint filers in 2026. That opens roughly $110,000 more of conversion room per year at a 22% marginal cost, still cheaper than the 24% or 25%-plus effective rates most large 401(k) balances trigger once RMDs, Social Security, and IRMAA all fire at once.

The Medicare piece is where couples over-convert and get burned. Part B is $202.90 a month in 2026 at the standard premium, but the first IRMAA surcharge kicks in for joint filers with MAGI above $218,000, and premiums climb from there. Because IRMAA uses a two-year lookback, the tax return filed at age 63 sets Part B and Part D premiums at age 65. The return at age 64 sets premiums at age 66.

Only the first gap year, age 62, is truly IRMAA-free. Aggressive conversions belong there. In years two and three, keep MAGI under the $218,000 joint threshold unless the long-term savings clearly outweigh a year or two of surcharges. A $30,000 conversion that pushes MAGI $1 over the line can add hundreds of dollars per person per month in future Part B and Part D premiums.

Model each gap year separately. Age 62 is the year to convert most aggressively. At ages 63 and 64, cap MAGI just under $218,000 to preserve the standard $202.90 Part B premium at 65 and 66.

Pair conversions with a cash bucket. With the 10-year Treasury near 5%, a short Treasury ladder can fund living expenses so conversion dollars actually leave the pretax account instead of being siphoned off to pay the tax bill.

Respect the new catch-up rule if either spouse still works part-time. For 2026, employees 50 and older who earned more than $150,000 in 2025 must route catch-up contributions to a Roth 401(k), which raises taxable income today but adds tax-free assets that pair well with the conversion plan.

The 2027 Social Security COLA is currently tracking near 3.3%, meaning the eventual benefit check, and the taxable-income problem it creates, keeps growing. The three gap years do not repeat. Used deliberately, they can shift a six-figure slice of the 401(k) into a Roth at a tax rate the couple will never see again (we sized up this exact window, between the last paycheck and the first RMD, in a free Roth guide here: The Roth Window).

One investment mistake could create big risks for your retirement. Many investors make the same critical errors: being too conservative, making big bets on "sure things," or paying excessive fees. Any of those blunders can endanger your hard-earned savings.

Now you can learn the mistakes even experienced investors make (and ways you can sidestep them before it's too late) with this new guide: 13 Retirement Mistakes and How to Avoid Them from Fisher Investments. (sponsor)

Contact editorial@247wallst.com for any questions or corrections.