How a Single Retiree’s 401(k) Income Above $75,000 in 2026 Cuts Into a New $6,000 Senior Deduction

Quick Read

• The One Big Beautiful Bill's $6,000 senior deduction phases out by 6 cents for every dollar of MAGI above $75,000, and it disappears entirely at $175,000 for single filers.

• That phaseout pushes the effective marginal rate to 23.32% inside the 22% bracket, and crossing the $109,000 IRMAA level can add $1,148 a year in Medicare surcharges.

• Evenly spreading withdrawals over multiple years and keeping Roth conversions below the IRMAA cliff can help preserve more deductions before the senior deduction ends in 2029.

• Big 401(k) choices often get made once and then never revisited: when to roll over the account, what investments to use, and when to begin withdrawals. That is the problem the free report, 401k & IRA Tips and Answers, is meant to solve. (Sponsor)

Consider a 66-year-old single retiree with $900,000 in a traditional 401(k). In 2026, the retiree withdraws $80,000 and has no other income. That withdrawal moves past an income line many retirees have never noticed, where every added dollar starts to increase federal tax costs.

Why the $75,000 Threshold Changes a 2026 Tax Bill

The One Big Beautiful Bill introduced a $6,000 deduction for each taxpayer who reaches age 65 by the end of the year. It applies only to tax years beginning before January 1, 2029.

The deduction is reduced by 6% of modified adjusted gross income, or MAGI, above $75,000 for single filers. In this case, MAGI is essentially adjusted gross income, with only a few foreign-income add-backs.

Every dollar taken from a traditional 401(k) counts toward MAGI. At $80,000, the retiree still receives a $5,700 senior deduction.

If the withdrawal rises to $100,000, the deduction drops to $4,500. At $175,000, it is fully eliminated.

The Hidden 23% Rate Inside the 22% Bracket

From $75,000 to $175,000, each additional dollar of income removes six cents of the deduction, which means each dollar withdrawn effectively adds $1.06 of taxable income.

For single filers in 2026, the 22% bracket begins above $50,400 of taxable income. Inside that bracket, the true marginal rate becomes 23.32%.

In the 24% bracket, the effective rate rises to 25.44%.

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Using our retiree as an example, increasing 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, compared with $4,400 at a flat 22% rate.

The $264 difference comes from the phaseout.

Medicare surcharges create an even sharper cliff. The income-related monthly adjustment amount, or IRMAA, is generally based on MAGI from two years earlier. Income in 2026 affects premiums in 2028.

Under 2026 Medicare rules, a single filer above $109,000 pays an extra $81.20 per month for Part B and $14.50 for Part D.

Crossing that level adds $1,148.40 a year in surcharges at current rates. Premiums and income limits for 2028 will be different.

This phaseout adds another layer to retirees’ tax bills. It is one of several income-triggered rules, including nine we documented in a free guide called The Retiree's Tax Trap Map.

Three Deductions This Retiree Can Stack

Here is how the $80,000 withdrawal is taxed in practice:

1. Standard deduction: $16,100 for single filers in 2026. Anyone who does not itemize gets this amount, regardless of income.

2. Age-65 addition: $2,050 for a single filer age 65 or older. This is added on top of the standard deduction and is not subject to an income test.

3. Senior deduction: $5,700 after the phaseout. This is the only one of the three that shrinks as withdrawals rise.

Together, those deductions total $23,850, which leaves $56,150 of taxable income. Keep MAGI and taxable income separate: the phaseout and IRMAA are based on MAGI, which in this case is the full $80,000, and deductions do not reduce it. Additional itemized deductions can lower taxable income, but they cannot restore the age-based deduction.

Steps to Consider Before Year-End

Our retiree controls the timing. Required minimum distributions do not begin until age 75 for anyone born in 1960 or later, so every withdrawal before then is elective.

1. Spread withdrawals evenly. Taking $160,000 in one year and nothing in the next lowers that year's senior deduction to $900, and it also triggers IRMAA two years later. Taking $80,000 in each year preserves $11,400 of deductions across the two years.

2. Plan Roth conversions with the IRMAA threshold in mind, not just the $75,000 senior-deduction line. The phaseout costs only pennies per dollar, while the premium surcharge acts like 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 the 2026 income year to set 2028 premiums, based on thresholds announced closer to that time.

3. Work out MAGI before making the final withdrawal of the year. When checking IRMAA, include 401(k) withdrawals, conversions, taxable interest, any taxable Social Security, and tax-exempt interest. If the total is near the applicable Medicare threshold, it may make sense to move a December withdrawal into January. IRMAA thresholds generally rise with inflation, so review the published 2028 figures once they are available.

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