Medicare at 65 While Still Working?

You turn 65, you’re still working, you have good coverage through your job. Do you have to sign up for Medicare anyway? Usually no, and the people who panic-enroll often make their lives worse and more expensive. But there are two traps here that don’t announce themselves, and both can cost you for years.

The size of your employer changes everything

The whole question hinges on one number: how many people work at your company.

If your employer has 20 or more employees, your group plan stays your primary coverage. You can delay Medicare Part B, the part that covers doctors and outpatient care and charges a monthly premium, until you actually retire. There’s a Special Enrollment Period waiting for you when you leave, so you sign up then with no late penalty. For 2026 the standard Part B premium is $202.90 a month, money there’s no reason to start paying while a solid group plan is doing the job.

If your employer has fewer than 20 employees, the rules flip on you. Medicare becomes primary whether you enroll or not, and your group plan may pay little or nothing on claims it assumes Medicare already covered. Skip enrollment in that situation and you can be left with bills you thought were insured. So the first move isn’t a gut call. It’s a phone call to HR to ask how Medicare coordinates with your specific plan. The enrollment timing decision lives or dies on that answer.

The HSA trap that catches high earners

Here’s the one that surprises people with real money, and it’s pure second-order. The moment you enroll in any part of Medicare, including the “free” Part A that most people grab reflexively at 65, you can no longer contribute to a Health Savings Account.

So if you’re still working, still on a high-deductible plan, and still funding your HSA, signing up for Part A quietly kills one of the best tax shelters in the code. Worse, when you eventually claim Social Security, enrollment in Part A becomes automatic and can backdate up to six months. Keep contributing into that window and you’ve made excess contributions the IRS will want unwound. Anyone planning to fund an HSA past 65 has to stop contributions before Medicare starts to stay clean.

When enrolling at 65 is the right move

I’m absolute on checking the rules and humble on the verdict, because plenty of people should enroll on time.

Enroll at 65 if you work for a small employer and Medicare is primary. Enroll if your group coverage is thin or pricey and Medicare plus a supplement would genuinely cover you better. And enroll if you’re not contributing to an HSA anyway, in which case grabbing premium-free Part A is usually harmless. The penalty for getting Part B wrong isn’t a one-time slap. It’s a surcharge added to your premium for the rest of your life, 10% for every year you should have been enrolled and weren’t.

My take

This is a decision where the autopilot answer and the right answer often disagree. Don’t enroll out of reflex, and don’t skip out of reflex either. Call HR, get the employee count and the coordination rule in plain language, and check your HSA before you touch Part A.

Two questions, asked before your birthday, save you from a lifetime surcharge and a blown tax shelter. Cheap insurance against an expensive mistake.