Every Dollar of 401(k) Income Over $75,000 in 2026 Erases 6 Cents of a Single Retiree’s New $6,000 Senior Deduction
A little-known income threshold in the 2026 tax code quietly reshapes retirement math for anyone drawing from a traditional 401(k), and crossing it by even a dollar sets off a chain reaction that hits your tax bill from more than…
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Picture a 66-year-old single retiree with $900,000 in a traditional 401(k). In 2026 this retiree draws $80,000 and has no other income. That withdrawal lands just past an income line many retirees have never heard of, where each additional dollar withdrawn starts costing more in federal tax.
How the $75,000 Line Rewrites Your 2026 Tax Bill
The One Big Beautiful Bill created a $6,000 deduction for each taxpayer who turns 65 by year end. It covers only tax years that begin before January 1, 2029.
The deduction shrinks by 6% of modified adjusted gross income (MAGI) above $75,000 for a single filer. MAGI here is simply your adjusted gross income, with a few foreign-income add-backs.
Every traditional 401(k) dollar counts toward MAGI. At $80,000, our retiree keeps a $5,700 senior deduction.
Raise the withdrawal to $100,000 and it falls to $4,500. At $175,000 it is gone entirely.
A Hidden 23% Rate Inside the 22% Bracket
Between $75,000 and $175,000, each extra dollar of income wipes out six cents of deduction, so each dollar you withdraw adds $1.06 of taxable income.
For single filers in 2026, the 22% bracket starts above $50,400 of taxable income. Inside it, your real marginal rate becomes 23.32%.
In the 24% bracket, it jumps to 25.44%.
Run it on our retiree. Raising the 2026 withdrawal from $80,000 to $100,000 lifts federal tax from about $7,065 to $11,729.
That extra $20,000 costs $4,664, against $4,400 at a flat 22%.
The $264 gap is the phaseout at work.
Medicare surcharges are a far bigger cliff. The income-related monthly adjustment amount (IRMAA) is generally based on MAGI from two years earlier. Your 2026 income will determine your 2028 premiums.
Under 2026 Medicare rules, a single filer above $109,000 pays an extra $81.20 a month for Part B and $14.50 for Part D.
Crossing that threshold adds $1,148.40 a year in surcharges under today’s rates. The income limits and premiums for 2028 will be different.
This phaseout adds another layer to retirees’ tax bills. It is one of a growing set of income-triggered rules (we documented nine of them, this one included, in a free guide here: The Retiree’s Tax Trap Map).
Three Deductions This Retiree Can Stack in 2026
Here is how the $80,000 withdrawal actually gets taxed:
- Standard deduction: $16,100 for single filers in 2026. Every filer who skips itemizing gets this amount, regardless of income.
- Age-65 addition: $2,050 for a single filer 65 or older. It sits on top of the standard deduction and has no income test.
- Senior deduction: $5,700 after the phaseout. This is the only one of the three that reduces as your withdrawals grow.
Together these deductions total $23,850, leaving $56,150 of taxable income. Keep MAGI and taxable income separate in your head. The phaseout and IRMAA both run off MAGI, which here is the full $80,000, and deductions never reduce it. Extra itemized deductions lower your taxable income, but they cannot restore any of that age-based deduction.
Moves to Make Before the Year Closes
Our retiree controls the timing. Required minimum distributions start at 75 for anyone born in 1960 or later. Every withdrawal before then is a choice.
- Spread withdrawals equally. A $160,000 withdrawal in one year followed by nothing the next reduces that year’s senior deduction to $900. It also triggers IRMAA two years later. Taking $80,000 in each year keeps $11,400 of deductions across the two years.
- Size Roth conversions with the IRMAA line in mind, not just the $75,000 senior-deduction threshold. The phaseout costs pennies on the dollar, while the premium surcharge is a cliff. With $80,000 already withdrawn, a $29,000 Roth conversion brings MAGI to $109,000, the current Medicare surcharge threshold for single filers. Medicare will use her 2026 income to determine her 2028 premiums, based on thresholds announced closer to that year.
- Calculate your MAGI before your last withdrawal of the year. Add up 401(k) withdrawals, conversions, taxable interest, any taxable Social Security and tax-exempt interest when checking IRMAA. If the total lands near the applicable Medicare threshold, consider pushing the December withdrawal into January. IRMAA thresholds generally rise with inflation, so check the 2028 figures once they are published.
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Gerelyn Terzo is the author of dividend investing handbook "Dividend Investing Strategies: How to Have Your Cake & Eat It Too." A veteran financial journalist, she covers agri-finance for outlets like Global AgInvesting and the broader stock market and personal finance for 24/7 Wall Street. She began at CNBC and later helped launch Fox Business in New York. Gerelyn currently resides in Woodland Park, Colorado and dabbles in nature photography as a hobby.
