Still working at 65? Here’s what to do about Medicare.

Published July 10, 2026 · By Erik Roti, Options.Health

Turning 65 doesn’t automatically mean it’s time to enroll in Medicare — but for a meaningful share of people still working, it does. The deciding factor almost always comes down to one thing: how many employees your company has.

The employer size test

If your employer has 20 or more employees, your group health plan is generally considered primary and Medicare would be secondary if you enrolled — which means you can typically delay Part B without a late penalty, for as long as you’re actively covered by that employer plan. If your employer has fewer than 20 employees, Medicare usually becomes the primary payer at 65 regardless of your employer coverage, which means delaying enrollment can leave real gaps, since the employer plan may pay only what it would if you had Medicare, whether you’re enrolled or not.

Why many people enroll in Part A anyway

Part A is premium-free for most people with enough work history, so it’s common to enroll in Part A at 65 even while delaying Part B and staying on an employer plan — there’s rarely a downside to the free piece. Part B carries a monthly premium, and that’s the piece worth delaying if your employer plan qualifies as primary, largely because paying for two overlapping coverages rarely makes sense.

The HSA complication

If you contribute to a Health Savings Account, enrolling in any part of Medicare — including the free Part A — ends your HSA eligibility going forward. It gets trickier if you delay claiming Social Security: enrolling in Social Security after 65 triggers retroactive Part A enrollment of up to six months, which can retroactively conflict with HSA contributions made during that window. If you’re actively contributing to an HSA and plan to delay Social Security, stopping contributions a few months ahead of enrolling is usually the safer move.

COBRA doesn’t count as active coverage

This is the mistake that catches people most often: COBRA continuation coverage is not treated the same as active employer coverage for Medicare enrollment purposes. If your active employment ends and you go on COBRA instead of Medicare, your Special Enrollment Period clock is generally already running, and waiting until COBRA runs out to enroll can mean a late penalty that follows you for the rest of your Medicare coverage.