A 73-year-old with $1.5 million in a traditional 401(k) just hit the year required minimum distributions begin. The first check to the IRS looks manageable. The next twelve do not. Ordinary income tax, Social Security taxation, and Medicare surcharges stack in a way most retirees never model until the bill arrives.
The scenario is common enough that variants appear on the Bogleheads and r/retirement forums every few weeks: single filer, high balance, modest Social Security, no Roth money, and a portfolio still weighted toward growth. The reader wants to know what the RMDs actually cost, cumulatively, once every downstream effect is counted.
The First RMD Is the Smallest One
At 73, the IRS Uniform Lifetime Table divisor is 26.5. On a $1.5 million balance, that produces a first RMD of roughly $56,600. Social Security of around $36,000 stacks on top, with up to 85% becoming taxable.
After the $16,100 standard deduction for single filers and the extra senior deduction, taxable income lands near $69,000. That falls almost entirely in the 22% bracket, which starts at $50,400 for single filers. Federal tax runs roughly $10,000.
The divisor is what changes the picture. At 78 it drops to 21.1. If the portfolio compounds at a modest pace, the mandated withdrawal climbs above $71,000. By the early 80s, the divisor is under 19, and the RMD alone can push MAGI past $100,000 even before Social Security is counted.
Where the $280,000 Actually Comes From
Three costs move together once RMDs start.
Federal income tax on the withdrawals themselves runs 22% to 24% on most of the balance withdrawn, because RMDs sit on top of Social Security and any pension or dividend income. Over roughly a dozen years of distributions from a $1.5 million starting balance, that alone accounts for the bulk of the cumulative bill.
The Social Security tax cascade adds the second layer. Once combined income exceeds $34,000 for a single filer, 85% of benefits become taxable. A retiree who could have kept only 50% of benefits taxable, or none, effectively pays income tax on an extra $10,000 to $15,000 every year the RMD is drawn.
IRMAA is the third layer, and the one that catches retirees off guard because of the two year lookback. A single filer with MAGI above $109,000 pays the first Medicare surcharge tier, worth $1,148 per year in combined Part B and Part D premiums. Higher tiers escalate from there. A single large RMD or a poorly timed Roth conversion can trip the threshold and lock in that surcharge for a full year, two years later.
Add the three streams across the RMD horizon on a $1.5 million balance and cumulative federal tax plus Medicare surcharges plus the tax on newly taxable Social Security lands near $280,000. That number is the base case for anyone who leaves the traditional 401(k) untouched from 73 onward.
Model Your Own Withdrawal Path
Because the interactions between RMDs, Social Security taxation, and IRMAA thresholds are highly individual, readers should run their own numbers before assuming the base case applies. Fidelity’s Retirement Income Planner and Schwab’s retirement withdrawal calculator both model multi year withdrawal sequences and let users test how a Roth conversion or QCD changes MAGI in later years.
Three Moves That Actually Change the Math
- Use Qualified Charitable Distributions to satisfy the RMD. The 2026 QCD limit is $111,000 per person. A QCD counts toward the RMD but never hits AGI, which means it does not push Social Security into higher taxation and does not raise MAGI for IRMAA. For charitably inclined retirees, this is the single most efficient tool available.
- Run partial Roth conversions in the low income window before RMDs peak. Filling the 22% or 24% bracket in the early 70s can shrink the taxable balance before divisors get punishing. Keep each conversion below the next IRMAA threshold, because Medicare uses MAGI from two years back. A conversion at 73 shows up on the 2028 premium.
- Coordinate withdrawals with the 2.8% Social Security COLA and current bond yields. The 10 year Treasury near 4.6% means the fixed income side of the portfolio can generate taxable interest that stacks with the RMD. Holding Treasuries or municipal alternatives in the right account can pull MAGI back under the first IRMAA line.
The interactions are what drive the cost. Model the next five years of MAGI now, not the first RMD in isolation, and the $280,000 stops being inevitable.
Contact [email protected] for any questions or corrections.
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