Medicare's late enrollment penalties aren't a one-time fee — they're typically permanent additions to your premium. The good news is they're entirely avoidable once you understand how they work.
The Part B Penalty
If you don't sign up for Part B when you're first eligible — and don't qualify for a Special Enrollment Period through active employer coverage — your premium can increase by 10% for each full 12-month period you were eligible but didn't enroll. That increase generally applies for as long as you have Part B, not just for a year or two.
The Part D Penalty
The prescription drug penalty works differently but is just as long-lasting. It's calculated as 1% of the "national base beneficiary premium" for every full month you went without Part D or other creditable prescription drug coverage after your Initial Enrollment Period ended. Like the Part B penalty, this typically sticks with you for as long as you have Part D coverage.
The Exception That Trips People Up
Both penalties can be avoided if you have "creditable coverage" — generally, coverage through a current employer that's at least as good as Medicare's. The catch is that not all employer or retiree coverage qualifies as creditable, and the rules depend on employer size. Assuming your coverage is creditable without confirming it in writing is one of the most common — and costly — mistakes people make.
Quick Takeaways
- Part B penalty: roughly 10% per 12-month period of eligibility you didn't enroll, generally permanent.
- Part D penalty: about 1% of the national base premium per month without creditable coverage, generally permanent.
- Active employer coverage can delay enrollment penalty-free — but confirm it's "creditable" in writing.
- When employer coverage ends, you typically get a limited Special Enrollment Period to sign up without penalty — don't let it lapse.
If You Think You Might Already Have a Gap
If you're not sure whether you have a coverage gap, or whether your current or past employer coverage was creditable, that's worth sorting out sooner rather than later — the penalty calculation is based on actual time without coverage, so gaps don't fix themselves by waiting.
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