A 73 Year Old With $1.6 Million in a Traditional 401(k) Faces a $60,400 First RMD That Quietly Triggers an IRMAA Surcharge

A single retiree turns 73 this year sitting on $1.6 million in a traditional 401(k) and a $3,000 monthly Social Security check. The first required minimum distribution is no longer a future problem. It lands in 2026, and the size of it reshapes everything that follows: the tax bracket, the Medicare premium two years out, and the room left for any Roth conversion still on the table.

The arithmetic is the easy part. The trap sits one threshold away.

The first RMD, in plain dollars

The IRS Uniform Lifetime Table assigns a distribution period of 26.5 at age 73. Divide the prior year-end balance of $1,600,000 by that figure and the first RMD lands at $60,377, call it $60,400. That entire amount is ordinary income, stacked on top of the Social Security check the moment the funds leave the account.

With provisional income this high, 85% of the $36,000 annual Social Security benefit becomes taxable, adding $30,600 to the pile. Gross income before deductions comes to roughly $91,000. Subtract the 2026 single standard deduction of $16,100 and the $2,050 additional deduction available to single filers aged 65 and older, and taxable income lands near $72,850. That sits squarely inside the 22% bracket, which for single filers spans $50,400 to $105,700 in 2026.

One more layer of recent tax law is worth understanding. The One Big Beautiful Bill Act, signed on July 4, 2025, created a new $6,000 above-the-line deduction for taxpayers aged 65 and older, available for tax years 2025 through 2028 and claimable whether a filer itemizes or takes the standard deduction. The catch: the deduction phases out at a 6% rate for single filers with MAGI above $75,000 and disappears entirely at $175,000. With MAGI near $91,000, this retiree clears the $75,000 floor by roughly $16,000, eroding most of the benefit before it can be claimed. The remaining partial deduction may trim a few hundred dollars from the tax bill, though it does nothing to move the IRMAA needle. According to the Tax Policy Center, fewer than half of older adults actually benefit from this deduction, with middle-income seniors in the phase-out range seeing an average reduction of only about $220 to $300.

So far, predictable. The RMD was coming either way, and the first year tax hit is manageable.

Where the Medicare trap opens

Medicare IRMAA is calculated on modified adjusted gross income from two years earlier. The 2026 RMD lands on the 2026 return, which becomes the income base for the 2028 Part B premium. The first IRMAA threshold for a single filer is $109,000 in MAGI. Below it, the standard Part B premium is $202.90 per month.

A MAGI near $91,000 clears the $109,000 line with about $18,000 of cushion. But a single decision can vaporize that buffer: a $25,000 Roth conversion in the same year, a capital gain from portfolio rebalancing, or simply a larger 401(k) balance the following year as the divisor continues to shrink. Cross $109,000 and the first surcharge tier activates, adding $81.20 per month to Part B and bringing the total to $284.10, while a Part D surcharge of $14.50 per month rides alongside. Combined, Tier 1 IRMAA adds roughly $1,148 per year per beneficiary. None of that bill arrives until 2028, which is precisely why most retirees never see it coming.

Two tiers up, at MAGI above $137,000, the Part B premium climbs to $405.80 per month. The IRMAA cliff is among the steepest effective tax rates in the entire code: a single dollar over any threshold triggers the full surcharge for that tier, for the entire year.

What actually moves the outcome

The 401(k) balance grows with the market, and the RMD divisor falls every year. By age 80 the divisor reaches 20.2, which on a balance in this range pushes the RMD past $80,000 and the MAGI past $109,000 on its own, without any conversions or capital gains required. The clock is running from day one. One additional timing note: the IRS permits delaying the very first RMD to April 1 of the year after turning 73, but doing so stacks two full distributions into that following calendar year, which typically inflates the tax bill and the IRMAA exposure more than simply taking the first distribution on schedule.

Three levers matter:

1. Qualified charitable distributions. A QCD allows a direct transfer from an IRA to a qualified charity. It counts toward the RMD and is excluded from taxable income entirely, with no need to itemize. The 2026 QCD limit is $111,000 per individual. For a charitably inclined retiree, a $20,000 QCD shaves that same amount off MAGI and creates real distance from the $109,000 IRMAA line. The critical detail: QCDs must originate from an IRA, not a 401(k). A retiree holding assets in a 401(k) needs to roll the account into a traditional IRA before this strategy is available.
2. Partial Roth conversions, strictly inside the 22% bracket and with the IRMAA cliff mapped first. A conversion done at 70 or 71, before RMDs begin, is a fundamentally different calculation than one done at 73 when the RMD has already consumed most of the bracket. After age 73, every dollar converted adds to MAGI and can push the Medicare surcharge into effect two years later.
3. Timing of discretionary income. Capital gains, large Roth conversions, and one-off withdrawals belong in years where combined MAGI stays clearly below $109,000. Alternatively, they can be concentrated in years where an IRMAA tier has already been crossed, because at that point the marginal cost of one more dollar inside the same tier is zero.

Action items before December 31

Pull the December 31, 2025 statement and divide by 26.5 to confirm the exact 2026 RMD. Project full-year MAGI including the taxable Social Security portion and any planned conversions or capital gain events, then measure the gap to $109,000. If that gap is under $15,000, the priority is rolling the 401(k) into a traditional IRA and routing a portion of the RMD through a QCD before taking any cash personally. The QCD only qualifies if the funds leave the IRA as a direct transfer to the charity, before any distribution reaches the account holder’s hands.

Editor’s note: This article was updated to include Tax Policy Center data showing that fewer than half of older adults benefit from the OBBBA $6,000 senior deduction, with middle-income seniors in the phase-out range averaging only $220 to $300 in tax relief. The age-80 RMD divisor was also corrected to 20.2 (the precise IRS Uniform Lifetime Table value), and context was added on why delaying the first RMD to April 1 of the following year typically worsens both the tax bill and the IRMAA exposure.

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