Retirees With Over $1.2 Million in a Traditional 401(k) Are Being Warned About This Tax Bomb at 73 – 24/7 Wall St.

Picture a 70-year-old single retiree sitting on $1.2 million in a traditional 401(k), drawing $3,400 a month from Social Security and feeling well prepared. Three years from now, the IRS reaches into that account whether the money is needed or not. The forced withdrawal, layered onto an unindexed 1984 income threshold, quietly adds roughly $11,000 to $13,000 of new federal tax to the return at 73 and sets the stage for Medicare surcharges a few years after that.

Threads on r/retirement frequently include retirees asking whether RMDs will really sting at this size of account. At $1.2 million in pre-tax dollars, the answer is yes, and the mechanics are worth understanding before age 72.

The First RMD Is Bigger Than It Looks

The Uniform Lifetime Table divisor at 73 is 26.5. Applied to today’s $1.2 million balance, the first required minimum distribution runs about $45,000. Three years of 5% portfolio growth lift the balance closer to $1.39 million, pushing the first RMD nearer $52,000. That figure is not optional and lands as ordinary income.

Combine that RMD with $40,800 of annual Social Security benefits and adjusted gross income lands near $93,000. The single 65 and older standard deduction in 2026 is $18,100, the regular $16,100 plus the $2,000 age add-on, so taxable income drifts into the 22% to 24% federal bracket. The federal tax bill alone runs $11,000 to $13,000 before state taxes.

The 1984 Threshold Doing Real Damage

Up to 85% of Social Security benefits become taxable once combined income clears $34,000 for a single filer, a threshold written into law in 1984 and never indexed. CPI hit 330.3 in March 2026, with inflation still running above the Fed’s 2% target. Decades of price growth have hollowed that ceiling out completely.

At a $93,000 AGI, roughly $34,680 of the $40,800 benefit gets pulled into taxable income. The household ends up taxed on the dollars that funded Social Security in the first place, then taxed again on the benefit those dollars produced.

IRMAA Is the Trap That Trips Later

Medicare’s income-related surcharge has a two-year lookback, and the first single-filer tier in 2026 starts at $109,000 of MAGI. At $93,000, this scenario sits below the line for now. The problem is the trajectory. RMD divisors shrink every year while balances continue to compound, so RMDs commonly trip the first IRMAA bracket between ages 75 and 77. Once tripped, combined Part B and Part D surcharges run $1,148 to $6,936 a year on top of the standard about $203 monthly Part B premium.

What to Do in the Three Year Window

The window between 70 and 72 is the most valuable tax-planning real estate this retiree owns.

1. Run Roth conversions under the $109,000 MAGI line. Annual conversions of $40,000 to $50,000 from ages 70 through 72 shrink the traditional balance before RMDs begin, lower future divisors, and avoid tripping IRMAA two years later. A cumulative shift of about $135,000 can drop the projected first RMD by roughly $5,000 a year.
2. Use QCDs as soon as the calendar allows. Once a retiree turns 70½, qualified charitable distributions of up to $111,000 in 2026 count toward RMDs without raising AGI. Even $5,000 to $10,000 a year keeps Social Security taxation and IRMAA math cleaner.
3. Avoid double-stacking the first RMD. The IRS permits delaying the first RMD until April 1 of the year after turning 73, but doing so forces two RMDs into a single tax year and usually trips IRMAA. Take the first RMD in the year of the 73rd birthday unless income that year is unusually low.

The 10-year Treasury at 4.4% offers a respectable bond yield for the cash these conversions throw off, and the federal funds rate has held at 3.75% since December 2025, giving short-term planning some predictability. Map the numbers against the 2026 IRS Uniform Lifetime Table and the CMS 2026 IRMAA tiers before December. A fee-only advisor pays for their fee if combined income is anywhere near the $109,000 line, because every dollar over it carries a marginal cost most retirees never see on a tax return.