The 73-year-old who logged into their 401(k) portal this April with a $1.3 million traditional balance found that the first required minimum distribution generates a roughly $19,800 tax bill, more than double what the federal income tax on the withdrawal alone would suggest. The withdrawal itself is the smallest piece of the cascade.
How $49,000 Becomes a $19,800 Liability
The IRS Uniform Lifetime Table divisor at age 73 is 26.5. A $1.3 million account produces a first RMD of $49,057. In the 22% federal bracket, which starts at $50,400 of taxable income for single filers in 2026, the withdrawal generates close to $10,800 in tax. That figure is what most pre-retirees plan around, and it is the figure that misleads them.
The cascade starts when the RMD lands in adjusted gross income. Provisional income clears the $34,000 single-filer threshold, which makes up to 85% of Social Security benefits taxable. For a retiree drawing the 2026 average benefit, after Social Security raised payments 2.8% this year, that conversion adds roughly $5,000 to the federal bill on income that was previously sheltered.
Medicare delivers the third layer. The 2026 standard Part B premium is $202.90. IRMAA surcharges activate above $109,000 in modified adjusted gross income for single filers and $218,000 for married couples. A single retiree pushed into Tier 1 by the RMD pays an extra $81.20 per month on Part B and $13.70 on Part D. State income tax, where applicable, adds another $2,000 to $3,000. Stacked up, the cascade lands near $19,800.
The Two-Year Lookback That Catches People
IRMAA tracks income from two years prior. The 2026 surcharge is anchored to the 2024 tax return. A retiree who ran a large Roth conversion in 2024, sold a rental property, or harvested capital gains is paying the Medicare bill in 2026 regardless of what current income looks like. The reverse also applies: any planning move executed in 2026 will hit Medicare premiums in 2028. The window to manage the next bill is closing now.
For perspective, the Bureau of Labor Statistics put average annual consumer expenditures at $78,535 in 2024. A $19,800 RMD tax bill consumes a full quarter of a typical household’s spending, paid out of an account the retiree may not have needed to touch yet.
Three Moves That Actually Change the Number
- Run qualified charitable distributions before the RMD deadline. A QCD up to $111,000 per person in 2026 sends dollars directly from an IRA (after a 401(k) rollover) to a 501(c)(3), satisfying the distribution requirement without raising AGI. A retiree who already gives $10,000 a year to a church, alumni fund, or hospital can route that gift as a QCD and erase $10,000 from the cascade. Federal tax, Social Security taxation, and the IRMAA trigger all shrink in the same motion.
- Stage Roth conversions in the gap years between retirement and age 73. Every dollar moved at 22% or 24% in the early 60s is a dollar that never appears in a future RMD divisor. Stop each year’s conversion just below the IRMAA breakpoints of $109,000 single or $218,000 joint, then resume in January.
- Reset withholding before December. RMDs can have federal tax withheld at the source, and the IRS treats that withholding as paid evenly across the year. A retiree who realizes in November that estimated payments are short can withhold 50% on the December RMD and avoid the underpayment penalty without filing amended quarterlies.
The 10-year Treasury yield near 4.5% offers a conservative reinvestment option for RMD proceeds the retiree does not need to spend, but the tax bill clears first regardless. The decision worth making is which dollars leave the 401(k), and in what order, not whether they leave at all.
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