Missing your Medicare enrollment window doesn’t just mean a delay in coverage — for Part B and Part D specifically, it can mean a permanent increase to your premium, calculated based on how long you went without coverage. Understanding exactly how these penalties work is one of the most practical things you can do before your enrollment window arrives.
The Part B Late Enrollment Penalty
If you don’t enroll in Part B when you’re first eligible, and you don’t qualify for a Special Enrollment Period, your Part B premium generally increases by 10% for each full 12-month period you were eligible but didn’t enroll. This isn’t a one-time fee — it’s added to your monthly premium for as long as you have Part B, which for most people means indefinitely.
Example: if you delayed Part B enrollment by 24 months (two full 12-month periods) without qualifying coverage, your premium would generally be 20% higher than the standard premium — for as long as you have Part B.
This penalty is calculated based on the standard Part B premium in effect at the time, so the actual dollar amount can shift slightly as the standard premium changes each year, even though the percentage itself stays fixed once established.
The Part D Late Enrollment Penalty
The Part D penalty works differently. If you go 63 or more continuous days without creditable prescription drug coverage after your Initial Enrollment Period ends, you can face a penalty calculated as roughly 1% of the national base beneficiary premium for each full month you went without that coverage, rounded to the nearest 10 cents. Like the Part B penalty, it’s added to your monthly Part D premium for as long as you have Part D coverage — not a one-time charge.
“Creditable coverage” means drug coverage that’s expected to pay, on average, at least as much as Medicare’s standard Part D coverage — this could be coverage through a current employer, for instance, not just a Medicare-specific plan.
How to Calculate Your Potential Penalty
For Part B, the math is straightforward: count the full 12-month periods between when you became eligible and when you actually enrolled (excluding any time covered by qualifying employer coverage or a Special Enrollment Period), and multiply by 10%.
For Part D, count the full months without creditable coverage since your Initial Enrollment Period ended, and multiply by roughly 1% of the current national base beneficiary premium. Because that base premium can change annually, the exact penalty amount isn’t perfectly static year to year even for a fixed number of uncovered months, though the percentage-based calculation itself remains consistent.
When Penalties Don’t Apply
A few common situations where you can delay enrollment without triggering a penalty:
- Qualifying employer coverage. If you or a spouse have coverage through a current employer with 20 or more employees, you can generally delay Part B without penalty, as long as you enroll within 8 months after that employer coverage ends (this is a Special Enrollment Period, distinct from your Initial Enrollment Period).
- Creditable drug coverage. If your employer or other coverage counts as creditable for Part D purposes, you can delay Part D enrollment without a penalty, as long as you enroll within 63 days of that coverage ending.
- VA health benefits. Veterans with VA health coverage should check their specific situation carefully — VA coverage doesn’t automatically count as creditable coverage for Medicare purposes in every case, so this is worth confirming directly rather than assuming.
If you’re still working and unsure whether your employer coverage qualifies, see our full breakdown of how Medicare interacts with employer coverage before making a decision either way.
How to Dispute a Penalty You Think Is Wrong
If you believe a late enrollment penalty was calculated incorrectly — for instance, if you had creditable coverage that wasn’t properly documented — you can request a reconsideration. For Part B penalties, this generally goes through the Social Security Administration; for Part D penalties, through your specific Part D plan, which is required to provide a review process. Having documentation of your prior coverage (dates, and confirmation it was creditable) makes this process significantly smoother.
Why These Penalties Are Worth Taking Seriously
Because both penalties are permanent additions to your premium — not one-time fees — even a relatively short enrollment gap can add up to real money over the years you have Medicare coverage. This is exactly why enrollment timing gets its own dedicated attention in our Top 7 Medicare Mistakes guide, and why understanding your Initial Enrollment Period and Special Enrollment Period options in our full enrollment guide is worth doing before you need it, not after.
For the current 2026 premium figures these penalty calculations are based on, see our complete cost breakdown.
Not Sure Where You Stand?
Kayla Price is a licensed insurance agent (NPN 18530055) who can help you figure out your enrollment timeline and whether a penalty applies to your situation. Call (866) 648-1578 for a free, no-pressure review.