The RMD Tax Trap That Turns $260,000 in 401(k) Deferrals Into a $700,000 Problem

"Every marginal dollar deferred at 56 sits in the account for roughly 17 years before required minimum distributions force it out. At a 6% annual return, $1 today grows to almost $3 of fully taxable RMD income at 73. That $260,000 of fresh deferrals becomes closer to $700,000 of ordinary-income withdrawals stretched across the RMD years."

"The bracket on the way out is the punchline. A retired couple drawing Social Security, pensions, and RMDs from a stack that has compounded for two decades rarely lands in a 12% bracket. Federal tax on those RMDs typically runs 22% to 24%, plus state. Stack the Social Security taxation trigger (up to 85% of benefits become taxable once provisional income clears the threshold) and IRMAA Medicare surcharges of $70 to $400 per month per spouse on top, and the effective marginal rate on the last RMD dollar can sit near 40%."

"The arbitrage between today's 38% deduction and tomorrow's 35% to 40% all-in rate is, at best, a wash. At worst, it is negative."

"Once the employer match is captured, the case for routing the next dollar to a taxable brokerage account rests on structural tax-code features: Liquidity before 59.5. Retiring at 60 sti"

A dual-income couple with substantial traditional 401(k) balances plans to keep maximizing pre-tax contributions through age 60. Additional deferrals provide immediate tax savings at their current marginal rate. Those dollars then compound for roughly 17 years until required minimum distributions begin. The resulting withdrawals are ordinary income and often fall into higher effective tax rates in retirement due to Social Security taxation, Medicare IRMAA surcharges, and state taxes. The article argues that after capturing employer match, directing additional savings to a taxable brokerage can improve outcomes by providing earlier liquidity, enabling tax-efficient capital gains treatment, and reducing reliance on large RMD-driven ordinary income.

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