Still Working Past 65? Do You Need to Enroll in Medicare?

Turning 65 doesn't automatically mean signing up for Medicare, especially if you're still working with health coverage through your job. But whether you can safely wait — or need to enroll right away — comes down to one specific detail: the size of your employer.

The single most important question: how many employees?

Medicare's rules split into two very different paths depending on your employer's size, and getting this wrong is the single most common (and costly) mistake among people working past 65.

• 20 or more employees: Your employer plan is generally considered primary. You can typically delay Medicare Part B without penalty for as long as you have that coverage.
• Fewer than 20 employees: Medicare generally becomes primary at 65. In most cases, you'll need to enroll during your Initial Enrollment Period to avoid a gap in coverage and a permanent late-enrollment penalty.

This count includes full-time, part-time, and seasonal employees across all of the employer's locations — not just your local office. Don't guess; ask your HR or benefits department directly, and get the answer in writing if you can.

If your employer has 20+ employees

You generally have a few options: keep just your employer coverage and delay Medicare, enroll in Medicare and drop the employer plan, or carry both. Many people in this situation still enroll in Part A, since it's usually premium-free if you or a spouse paid Medicare taxes for at least 10 years — there's little downside to having it as secondary coverage. Part B carries a monthly premium, so many people delay it until their employer coverage actually ends.

If your employer has fewer than 20 employees

Medicare typically becomes your primary coverage at 65 in this scenario, even if you keep working. Not enrolling in Part B during your Initial Enrollment Period usually means a gap where neither your employer plan nor Medicare is paying primary — and it can trigger the Part B late-enrollment penalty, which adds 10% to your premium for every 12-month period you were eligible but didn't enroll, permanently.

When you eventually stop working: your Special Enrollment Period

Once your employer coverage ends (or you stop working, whichever comes first), you get an 8-month Special Enrollment Period to sign up for Part B without penalty. A separate, shorter 2-month window applies if you want to enroll in a Medicare Advantage plan or a stand-alone Part D drug plan at that time. To avoid a coverage gap, most people aim to have Part B in place by the time their employer coverage actually ends, not after.

The HSA contribution trap

If you're contributing to a Health Savings Account (HSA), enrolling in any part of Medicare — even just premium-free Part A — makes you ineligible to contribute further. Some people are unexpectedly enrolled in Part A automatically once they start collecting Social Security, which can create a surprise HSA contribution problem. If you're still contributing to an HSA and plan to keep working past 65, this timing is worth planning around carefully.

Should you actually keep the employer plan, or switch to Medicare?

Even when you're allowed to delay Medicare, it isn't automatically the right move. It's worth comparing your employer plan's premium, deductible, and network against what Medicare (with or without a Medicare Advantage or Medigap plan) would actually cost and cover for your specific situation. Sometimes the employer plan wins; sometimes Medicare does. It depends on the numbers.