Employer Health Costs Are Projected to Jump 8.2%. At 65, Moving to Medicare Means Her HSA Contributions Have to Stop

A 65-year-old still working opens her benefits packet and sees the number every HR department is bracing for. Employer health-benefit costs per employee are projected to rise 8.2% in 2027, the steepest hike since 2003 and the fifth consecutive year of increases, according to preliminary results from Marsh’s 2026 National Survey of Employer-Sponsored Health Plans. To hold the increase even to that, 59% of employers plan cost-cutting changes to their health benefits. Without any mitigation, employers estimate their current plans would cost 11% more.

That is a cost-per-employee projection, not a forecast of what any one worker’s payroll deduction will do. But rising workplace costs give her a concrete reason to compare the company plan with Medicare and pick the cheaper one. That comparison is worth doing. The trap is what happens to her health savings account the moment she signs up.

This is a narrow, high-stakes window: someone who is 65, still covered by a large-employer plan, still funding an HSA, and now watching her share of costs climb. Anyone already enrolled in Medicare falls outside its scope.

Medicare Enrollment Mechanics

Enrollment in any part of Medicare, including premium-free Part A, ends HSA eligibility beginning with the month Medicare coverage takes effect.

It does not erase the whole year. Her annual contribution limit becomes prorated, counting one-twelfth for each month she was eligible. She can still deposit money after Medicare begins to cover those earlier eligible months, as long as employee and employer contributions together stay inside that prorated limit. IRS Publication 969 spells out how retroactive coverage factors into the calculation. Whatever is already in the account stays there, and she can spend it tax-free on qualified medical costs for the rest of her life.

Those final contributions can still be valuable. The HSA is the only account in the tax code with a triple tax break, though earlier contributions generally have more time to compound. Giving up the last of them to respond to rising workplace costs deserves a real calculation, especially once Medicare’s own costs enter the picture. The 2026 standard Part B premium is $202.90, up $17.90 from $185.00 in 2025, and that is before Part D, a Medigap policy, or any income-related surcharge.

The Trap Most People Miss

The subtler problem is timing. When someone files for Social Security after age 65, the Social Security Administration automatically enrolls her in Part A and backdates that enrollment up to six months, never earlier than the month she turned 65. She does not choose the effective date.

Those retroactive months come out of her eligibility calculation, which lowers the prorated limit after the fact. Contributions made during that stretch do not automatically become excess. Only the amount above the newly prorated limit does, and that froth is subject to income tax plus a 6% excise tax for each year it sits uncorrected.

The clean fix is to stop all HSA contributions, including the employer match, at least six months before she plans to claim Social Security or enroll in Medicare. If she wants to keep contributing through her full working year, she has to delay Social Security past that six-month buffer, not just delay Medicare.

Running the Actual Comparison

The fair comparison runs on total annual cost including the lost HSA tax break, plus any Income-Related Monthly Adjustment Amount (IRMAA) exposure on the Medicare side. The surcharge is not trivial at higher incomes. In 2026, the income-related adjustment begins above $109,000 in modified adjusted gross income (MAGI) for a single filer, and the top tier carries a total Part B premium of $689.90 per month. CMS has not yet published the 2027 amounts.

IRMAA runs on a two-year lookback, which is where people miscalculate. If she moves to Medicare in 2027, her 2025 return ordinarily sets that year’s surcharge. Her final full year of W-2 wages and any bonus would ordinarily land on her 2028 premium instead, two years after she stopped earning it.

Social Security income will not cushion much of that. The 2027 cost-of-living adjustment (COLA) is currently projected in the mid-3% range, with AARP’s estimate at the top of the spectrum. SSA announces the official figure in October.

Take Your Time

Here are some steps to take before signing on the dotted line:

1. Confirm the employer coverage is based on current employment and that the employer has at least 20 employees. Below that threshold, Medicare becomes primary and delaying Part B is no longer safe.
2. Ensure the plan is an HSA-qualified high-deductible plan. Otherwise, the contribution question is already settled.
3. Stop HSA contributions at least six months before filing for Social Security. Notify payroll in writing and confirm the employer contribution stops too. If Social Security is already filed, recalculate the prorated limit using the month Part A actually took effect, including its retroactive months.
4. Price the full Medicare stack, not just Part B. Add Part D, either Medigap Plan G or a Medicare Advantage plan, and any IRMAA surcharge her income two years back will trigger. Compare that annual total against her new employee cost share plus the value of the contributions she would forfeit.

The 8.2% projection is the reason to run the comparison. The HSA rule is the reason not to rush it.

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