Medicare while working: should you switch or keep your group plan?
Still covered through an employer at 65? Whether it makes sense to switch to Medicare depends on your plan, employer size, and real costs — and the answer isn't always obvious.
You turned 65, you're still working, and you have good coverage through your job (or your spouse's). Friends tell you that you "have to sign up for Medicare." A brochure says you'll be penalized if you wait. So which is it? For many people who are still working, the honest answer is: it depends — and a few specific facts decide it. Here's how to think it through without guessing.
Do you actually have to sign up at 65?
Not necessarily. If you have health coverage based on current, active employment, you're generally allowed to delay Part B without a late penalty and pick it up later when you retire. The "you must enroll at 65" warning is really aimed at people without active employer coverage. So the real question isn't whether you can wait — it's whether waiting is the better deal for your situation.
The one fact that changes everything: your employer's size
This is the fact most people don't know, and it reframes the whole decision:
- 20 or more employees: your group plan generally pays first and Medicare pays second. You can usually keep your group coverage and delay Part B (and its premium) safely, without penalty.
- Fewer than 20 employees: Medicare generally pays first, whether or not you've actually enrolled. If you delay Part B here, the group plan may only cover its small "secondary" share — leaving big bills unpaid. At a small employer, enrolling at 65 is usually the safer call.
Part A, Part B, and the HSA trap
Most people get Part A premium-free, so the instinct is "it's free, I'll just take it." That's fine for many — but not if you're contributing to a Health Savings Account (HSA). Once you're enrolled in any part of Medicare, including premium-free Part A, you can no longer contribute to an HSA. (You can still spend what's already in it.)
There's a second, sneakier version of this trap: when you claim Social Security at or after 65, Medicare grants Part A retroactively — up to six months back. Any HSA contributions you made during those months can become excess contributions with a tax consequence. If keeping your HSA matters, the usual guidance is to stop contributing about six months before you enroll in Medicare or start Social Security. This is a good one to run past a tax professional before you act.
Delaying Part B safely — and the clock that starts when you retire
If your large-employer coverage lets you delay Part B, you stay protected by a Special Enrollment Period: you can enroll anytime while you're still covered through active employment, and for up to 8 months after that employment or coverage ends. Done right, there's no penalty and no gap.
One critical caveat: COBRA and retiree coverage don't count as current-employment coverage. The 8-month clock starts when your active job ends, not when COBRA later runs out — so don't let COBRA lull you into missing the window.
Don't forget your prescriptions
If you delay Medicare's drug coverage, your job's drug plan needs to be "creditable" — expected to pay at least as much as a standard Medicare drug plan. Your employer must send you a notice each year confirming this; keep it. If your coverage isn't creditable and you go without for 63 days or more, you can pick up a permanent Part D penalty later.
How to actually compare your group plan and Medicare
When the rules allow you to choose, the decision comes down to real numbers and real life, not labels. Look at:
- Total cost: premiums plus what you actually pay out of pocket for the care and drugs you use — not just the premium.
- Your doctors and pharmacies: who's in-network under each option.
- Your prescriptions: how each option covers the specific drugs you take.
- Your HSA goals: whether continuing to contribute is worth more to you than starting Medicare now.
- Your spouse: if they're on your plan, how your choice affects their coverage.
None of this requires you to decide alone. Your state's free, unbiased State Health Insurance Assistance Program (SHIP) can walk through the rules with you — find yours at shiphelp.org or 1-877-839-2675 — and we're glad to compare your group plan against your Medicare options side by side, at no cost to start.
Key takeaways
- With active employer coverage, you can often delay Part B without penalty.
- Employer size is the deciding factor: 20+ employees usually lets you wait; fewer than 20 usually means enroll at 65.
- Taking even premium-free Part A ends your ability to contribute to an HSA.
- COBRA and retiree coverage don't extend your enrollment window.
- Compare total real cost, networks, and drug coverage — not just the premium.
This article is educational and reflects general rules drawn from Medicare.gov, CMS.gov, SSA.gov, and IRS guidance. It is not tax advice or a recommendation of a specific plan, and individual situations vary — please confirm details for your circumstances. Last reviewed: June 2026.