How Medicare Works When You Turn 65 But Keep Working

The Basics: Part A and Part B

Original Medicare has two main parts. Part A covers hospital stays, skilled nursing care, and hospice, and most people qualify for it premium-free if they or a spouse paid Medicare taxes for enough years while working. Part B covers doctor visits, outpatient care, and preventive services, and it comes with a monthly premium that's set each year.

Do You Need to Enroll in Medicare at 65 If You're Still Working?

Not necessarily — and this is where employer size matters. In general:

• If your employer has 20 or more employees, your group health plan is usually considered primary, and many people in this situation can delay Part B without a penalty until that coverage ends.
• If your employer has fewer than 20 employees, Medicare typically becomes the primary payer at 65, and delaying Part B enrollment can create real coverage gaps.

These are general patterns, not guarantees — retiree coverage, COBRA, union plans, and multi-employer plans can all work differently. This is exactly the kind of detail worth reviewing individually rather than assuming.

Should You Take Part A Even If You Keep Working?

Since Part A is usually premium-free, many people enroll in it at 65 even while still working and covered by an employer plan. The one major exception is if you're contributing to a Health Savings Account (HSA).

HSA Considerations

Enrolling in any part of Medicare, including premium-free Part A, makes you ineligible to keep contributing to an HSA. There's also a detail that catches people off guard: when you enroll in Part A after 65, that enrollment can be backdated up to six months (but not earlier than your 65th birthday month). If you're still contributing to an HSA during that lookback window, it can create a contribution problem you'll need to correct. If you're an active HSA contributor approaching 65, this is worth planning around before you enroll.

What Is Creditable Coverage, and Why It Matters

"Creditable coverage" means your employer or other coverage is considered at least as good as Medicare's. If your coverage is creditable, you can generally delay Medicare enrollment without facing a late penalty later. If it's not creditable, delaying can expose you to penalties down the road — so it's worth confirming this directly with your employer's benefits department rather than assuming.

Enrollment Timing If You Delay

If you delay Part B because of creditable employer coverage, you generally get a Special Enrollment Period of 8 months after that employment or coverage ends to sign up without a penalty. For a full breakdown of enrollment windows, see Medicare Enrollment Periods Explained.

Situations Where Enrolling at 65 May Still Make Sense

Even if you could technically delay, enrolling at 65 sometimes makes more sense — for example, if your employer plan has a high deductible, if you value the cost predictability Medicare can offer, or if your coverage situation is complicated (retiree coverage, COBRA, or a smaller employer plan that doesn't coordinate well with your circumstances). There's no single right answer here; it depends on your plan, your health needs, and your budget.

Late Enrollment Penalties

If you don't have creditable coverage and don't enroll in Part B when you're first eligible, a late enrollment penalty can apply: generally about 10% of the standard Part B premium for each full 12-month period you were eligible but didn't enroll. This penalty is typically added to your premium for as long as you have Part B — which is why understanding your specific timing matters so much before you decide to delay.

Related Reading

Medicare Advantage vs. Medicare Supplement → · Medicare Enrollment Periods Explained → · New to Medicare? → · How Working Past 65 Can Affect IRMAA →

Frequently Asked Questions