Still working at 65? The two Medicare decisions behind that birthday

If you're turning 65 and still working, you've probably heard both halves of the folklore: you have to sign up at 65, and don't sign up, your work plan is fine. Neither is a rule. What actually governs the decision is how your employer's plan and Medicare coordinate — and that is set mostly by employer size. Medicare's own working-past-65 page is the primary source worth reading before anything else.

Employer size decides who pays first

When you have both Medicare and employer coverage, one of them pays first — the primary payer — and the other may pick up part of what's left. If your employer has 20 or more employees, the group plan is generally primary and Medicare is secondary, which is why many people in that situation delay Part B without consequence. If your employer has fewer than 20 employees, Medicare is generally primary, and the group plan may pay very little until Medicare is in place. Delaying Part B there can leave you exposed for services the work plan assumes Medicare already paid. Same birthday, opposite right answer.

Two coverage types trip people up because they feel like employer coverage and aren't treated as it: COBRA and retiree coverage. Neither counts as coverage from current employment for these purposes.

If you delay, the window afterward is eight months

People who keep working past 65 with qualifying employer coverage generally get a Special Enrollment Period for Part A and Part B: eight months, beginning when the employment ends or the group coverage ends — whichever comes first. That last clause is the one that bites. If someone retires and rolls onto COBRA, the clock started at retirement, not when the COBRA runs out.

The Part B penalty is permanent, not a one-time fee

Miss the window without qualifying coverage and Part B carries a late-enrollment penalty of 10% for each full 12-month period you could have had Part B and didn't — added to the premium for as long as you have Part B, per Medicare's costs page. It isn't a fine you settle once; it's a permanent adjustment. That alone is why this decision is worth an afternoon.

Drug coverage is a separate test: “creditable”

Part D has its own timing and its own standard. Employer drug coverage lets you delay Part D penalty-free only if it is creditable — expected to pay, on average, at least as much as standard Medicare drug coverage. Your plan is required to tell you in writing each year whether it is. Keep that notice; it is the document that shows you were covered. If the coverage isn't creditable and you go without Part D, the Part D late-enrollment penalty accrues at 1% of the national base beneficiary premium for each month you went without.

The HSA wrinkle nobody mentions

If you contribute to a health savings account, enrolling in any part of Medicare — including premium-free Part A — ends your eligibility to keep contributing. And when you enroll after 65, Part A coverage can be backdated up to six months, which can retroactively turn otherwise-fine contributions into excess ones. If an HSA is part of your setup, sort the timing before you file anything.

Three questions, and the decision is mostly made

How many employees does your employer have? Is the drug coverage creditable — in writing? Are you still funding an HSA? Answer those and the Part B and Part D questions usually answer themselves. When the answers are mixed — a small employer, a spouse on the same plan, a retirement date mid-year — that's exactly the situation worth walking through with a licensed agent. The conversation is free, and there's no pressure in either direction.