Before You Take That Part-Time Job in Retirement: How a $1.4 Million 401(k) Can Cost You $2,297 in Medicare Premiums

A 66-year-old who retired at 64 with a $1.4 million 401(k) and a paid-off house took a part-time consulting role 18 months later because grocery and Medicare bills stopped feeling manageable. The 2026 Retirement Confidence Survey from EBRI found that 27% of current retirees are drawing income from paid work, and an AARP survey released in February reported that 7% of retirees re-entered the labor force in the prior six months alone, with 48% citing the need for money as the main reason.

Headline CPI sits at 330.3 in March, up 1.1% from a month earlier. Healthcare spending now runs at an annualized $3.74 trillion, up roughly $309 billion in 14 months. The personal savings rate has slid from 6.2% in early 2024 to 4.0% in the first quarter of 2026. With the federal funds rate at 3.75%, down 75 basis points from last spring, the cash and CD yields that subsidized 2024 retirement budgets are thinner. Going back to work fixes the cash flow problem but creates three new ones that the gross paycheck does not advertise.

The Earnings Test Before Full Retirement Age

A retiree collecting Social Security who is younger than full retirement age for the entire calendar year has $1 in benefits withheld for every $2 earned above $24,480 in 2026. In the year someone reaches FRA, the threshold rises to $65,160, and the withholding drops to $1 for every $3. Withheld benefits eventually return as a higher monthly check after FRA, but cash flow gets squeezed during exactly the years the wages were supposed to help.

The Social Security Taxation Cascade

A married couple pulling $40,000 from a traditional 401(k), $35,000 in Social Security, and $30,000 in new W-2 wages crosses well past the $32,000 joint combined-income threshold where benefits start being taxed and the $44,000 line where up to 85% becomes taxable. In the 22% federal bracket, the next dollar of wages does more than the 22 cents of direct tax. Each dollar can drag 85 cents of Social Security into taxable income, lifting the effective marginal rate above 30% before state tax. A side job paying $30,000 can net closer to $20,000 once the cascade is counted.

The IRMAA Two-Year Lookback

Wages earned in 2026 set Medicare premiums for 2028. Modified AGI is the trigger, and the brackets are unforgiving. Cross $109,001 single or $218,001 joint, and the Part B premium jumps from $202.90 to $284.10 a month. Add the Part D surcharge, and the total IRMAA cost reaches $1,148 per person, or $2,297 for a couple. Slide into Tier 2 above $137,000 single or $274,000 joint, and the annual bill grows to $2,886 per person. The retiree who unretires with even a modest $40,000 W-2 stacked on top of a 401(k) draw, and Social Security can push the household into the first tier in 2026 and receive the Medicare bill in 2028, after the temporary job has likely ended.

Stack a 22% federal bracket, Social Security taxation, and the first IRMAA tier together, and the effective marginal rate on the next dollar of W-2 wages approaches 40 cents.

What to Do Before Accepting the Job

Three moves to make before signing the offer letter:

1. Project household MAGI (Modified Adjusted Gross Income) for the calendar year, including W-2 income, 401(k) draws, and the taxable portion of Social Security, then compare against the $109,000 single / $218,000 joint IRMAA cliff. If projected MAGI lands within $5,000 of a tier line, deferring the wages into a pre-tax 401(k) at the new employer can keep the surcharge off the 2028 Medicare bill entirely.
2. Pause traditional 401(k) withdrawals while wages are coming in. Layering pre-tax distributions on top of W-2 income stacks ordinary income on ordinary income. If the household needs cash during working months, draw from a Roth or taxable brokerage account and resume traditional withdrawals after the paycheck stops.
3. If under FRA, file Form SSA-521 to withdraw the Social Security application within 12 months of first claiming. The option is available once per lifetime. After the 12-month window, voluntary suspension at FRA halts the earnings test and earns delayed retirement credits worth roughly 8% per year of waiting up to age 70.

The unretirement decision turns on whether the income, after the cascade, is worth what the same hours would buy in a different sequence: a Roth conversion year, a deferred Social Security claim, or a tax-aware withdrawal from accounts already paid for.