Working Past 65: How Medicare Fits With Employer Coverage

Last reviewed: July 2026

Why working past 65 changes the Medicare playbook

Turning 65 no longer means an automatic handoff to Medicare. Millions of Americans keep working — and keep employer health coverage — well past their 65th birthday. The rules for how Medicare fits alongside a job-based plan are workable once you know them, but they contain several traps with real dollar consequences: a lifetime Part B penalty, a tax problem for HSA contributors, and a COBRA misunderstanding that catches people every year. This guide walks through each one. If you are new to how Medicare is structured, our Medicare parts explained guide covers the basics of Parts A, B, C, and D.

Who pays first: the 20-employee rule

The central question is whether your employer plan pays your medical bills first (primary) or Medicare does. Federal Medicare Secondary Payer rules draw the line at employer size:

20 or more employees: the group health plan pays first and Medicare, if you have it, pays second. Your employer must offer workers 65 and older the same coverage it offers younger employees.
Fewer than 20 employees: Medicare pays first and the employer plan pays second. If you have not enrolled in Medicare, the plan may pay only the small share it would owe as a secondary payer — potentially leaving you exposed for the rest.

Two details matter. The coverage must be based on current employment — yours or your spouse's. And both full-time and part-time workers count toward the 20-employee threshold. If you work for a small employer, or you are not sure how your plan is classified (multi-employer plans have their own wrinkles), ask your benefits administrator in writing whether the plan pays primary or secondary to Medicare.

When you can safely delay Part B — and when you can't

Part B carries a monthly premium — the 2026 standard amount is $202.90, with higher-income enrollees paying more (see our Medicare costs for 2026 guide). That is a significant cost on top of employer premiums, and the rules let many working people wait:

You can generally delay Part B without penalty if you (or your spouse) are actively working and you are covered by that employer's group health plan, and the employer has 20 or more employees.
Delaying is risky if the employer has fewer than 20 employees, because Medicare is primary — going without Part B can mean going largely uninsured for outpatient care, and the delay can trigger a penalty later.

The penalty is worth taking seriously: for each full 12-month period you could have had Part B but did not sign up (and did not have job-based coverage that excused the delay), 10 percent is added to your monthly premium — usually for as long as you have Part B. Whether delaying makes sense depends on your employer's size, your plan's costs, and your household situation, so confirm your own status with your benefits office and Social Security before deciding.

Part A is usually straightforward — unless you have an HSA

Most people qualify for premium-free Part A through their own or a spouse's work history, so many workers enroll in Part A at 65 even while staying on the employer plan, letting it serve as secondary hospital coverage. Note that if you have started collecting Social Security benefits, you are enrolled in Part A automatically and cannot drop it without withdrawing your Social Security application. There is one big exception to that pattern, and it changes the math entirely: health savings accounts.

The HSA collision

Under IRS rules, you cannot contribute to a health savings account for any month you are enrolled in any part of Medicare — including premium-free Part A. If you want to keep making HSA contributions (including employer contributions), you must delay all parts of Medicare, which also means delaying Social Security benefits, since those trigger automatic Part A enrollment.

The trap is retroactivity. When you sign up for Part A after 65, coverage is backdated up to six months (though no earlier than the first month you were eligible for Medicare). HSA contributions made for those retroactive months count as excess contributions, and excess amounts left uncorrected are subject to a 6 percent excise tax for each year they remain in the account. The commonly cited safeguard is to stop HSA contributions about six months before you apply for Medicare or Social Security benefits after 65. Because the timing depends on your pay periods and application date, this is a good question for a tax professional or your SHIP counselor — see IRS Publication 969 in the sources below for the official rules.

The COBRA trap

This is one of the most expensive misunderstandings in all of Medicare. COBRA lets you continue your employer plan for a time after leaving a job — but COBRA is not coverage based on current employment. Neither is retiree coverage. That means:

Your 8-month window to sign up for Part B without penalty starts when employment ends (or the employment-based coverage ends, whichever comes first) — not when COBRA ends.
Keeping COBRA for 18 months and then trying to enroll in Part B can leave you past your window, facing both a coverage gap and a lifetime penalty. Losing COBRA does not qualify you for a Part B Special Enrollment Period (though losing creditable COBRA drug coverage can still open the short Part D window described below).
Once you are eligible for Medicare, COBRA typically pays secondary — so relying on COBRA alone can leave large bills unpaid.

If you are offered COBRA at or after 65, the clock that matters is your employment end date — not the COBRA end date.

Your Special Enrollment Period when work ends

When you (or your covered spouse) finally stop working, a Special Enrollment Period opens. You can sign up for Part B (and Part A, if you delayed it) while you are still covered by the employment-based plan, or during the 8 months after the employment or the coverage ends, whichever happens first — with no late penalty. Coverage can generally start the month after you sign up. Social Security's form CMS-L564, completed by the employer, documents that you had qualifying coverage. Our Medicare enrollment periods guide covers how this window fits alongside the others.

Drug coverage runs on a shorter clock. If your employer drug coverage was creditable (at least as good as standard Medicare drug coverage — your plan must tell you each year), you can join a Part D plan without penalty, but the Special Enrollment Period lasts only 2 full months after the month that coverage ends. Go 63 or more days without creditable drug coverage and a penalty accrues that usually lasts as long as you have Medicare drug coverage — roughly 1 percent of a national base premium for each month you waited. See our Part D drug coverage guide for how those plans work.

One more timing note: your one-time Medigap open enrollment window — six months with guaranteed access to any Medigap policy sold in your state — begins when you are 65 or older and enrolled in Part B. Delaying Part B while working also delays that window; enrolling in Part B early, on the other hand, starts the six-month clock even while you are still on the employer plan. Our Medigap basics guide explains how that window works.

Where to get free, unbiased help

The right move depends on your employer's size, your plan's costs and creditable-coverage status, your HSA, and your household — there is no one-size answer, and this guide cannot tell you what to do in your specific case. For personalized, no-cost help, contact your State Health Insurance Assistance Program (SHIP) at shiphelp.org, call 1-800-MEDICARE, or use the tools at medicare.gov. Your employer's benefits administrator and Social Security (for enrollment mechanics) round out the list. If cost is a concern once you do enroll, see our guide to help paying for Medicare.

Sources

This guide is for general education only and is not medical, legal, insurance, or financial advice. For decisions about your own coverage, use official sources or free help from your SHIP counselor.