Why Your 401(k) Could Trigger a Tax Bomb in Retirement (And What to Do Now)

Jeremy Phillips

Sat, May 2, 2026 astatine 7:16 AM CDT 5 min read

If you've spent 30 years funneling wealth into a 401(k) and feeling bully astir the taxation deduction, here's the portion cipher enactment connected the enrollment brochure: the IRS has been waiting patiently the full time. The measure comes owed the twelvemonth you deed RMD age, and it doesn't get alone. It drags Social Security taxation, superior gains rates, and Medicare premiums successful with it.

The big of the Retire SMART Podcast laid it retired cleanly connected Episode 407: "that forced taxation organisation successful the future, taxable income to you, could propulsion you into higher taxation limits, could marque your Social Security wage much tax." I've been penning astir status income mechanics for years now, and this is the azygous astir under-discussed hazard I spot successful pre-retiree portfolios.

What an RMD Actually Does to You

A required minimum organisation (RMD) is the magnitude the IRS forces you to propulsion retired of a accepted 401(k) oregon IRA each twelvemonth erstwhile you scope RMD age. You don't get to take whether to instrumentality it. You don't get to take however much. And each dollar lands connected your taxation instrumentality arsenic mean income.

Picture a retiree surviving comfortably connected Social Security and a humble brokerage account. Their taxable income is low. Their Social Security is mostly tax-free. Their semipermanent superior gains mightiness adjacent beryllium successful the 0% bracket. Then RMDs footwear successful and stack a six-figure forced withdrawal connected apical of everything else.

Four things hap astatine once:

1. Higher marginal bracket. The RMD pushes mean income up, sometimes 2 brackets successful a azygous year.

2. More Social Security gets taxed. Once provisional income crosses definite thresholds, up to 85% of your payment becomes taxable. The RMD is what shoves you across.

3. Capital gains rates jump. Long-term gains that would person been taxed astatine 0% oregon 15% tin abruptly deed 15% oregon 20% due to the fact that your taxable income is present stacked higher.

4. IRMAA shows up. The Income-Related Monthly Adjustment Amount is simply a Medicare surcharge connected Part B and Part D premiums for higher-income retirees. Cross a threshold by a azygous dollar and some you and your spouse wage more, often for 2 afloat years earlier it resets.

The Roth Conversion Case

The verdict: for astir retirees with meaningful accepted balances, doing thing is the costly choice. The big went further, saying "over 90% of the clip erstwhile we tally the analysis" a Roth conversion makes sense. Paying taxation present astatine a known rate, successful a model wherever your income is lower, beats paying an chartless aboriginal complaint connected a overmuch larger forced withdrawal that besides drags Social Security and Medicare costs on with it.