Health & Medicare
Medicare Part D Late Enrollment Penalty Calculator
Estimates based on MedicareFAQ's summary of CMS penalty rules, updated August 2026.
See how much a gap in prescription drug coverage will permanently add to your Part D premium.
Data sourced from MedicareFAQ (CMS penalty rules summary)
Your new monthly Part D premium
$0.00
How this is calculated
Source: MedicareFAQ summarizing CMS penalty rules (2026 national base beneficiary premium, penalty formula) · Last updated 2026-08-19 · See how we calculate this →
See how this compares to the medical-coverage penalty: Medicare Part B Late Enrollment Penalty Calculator (a separate penalty with its own 10%-per-12-months formula).
How the Part D late enrollment penalty is actually calculated
Medicare Part D has its own permanent late enrollment penalty, separate from the Part B penalty, for anyone who goes without Part D or other creditable prescription drug coverage after first becoming eligible.
Unlike Part B, which counts in whole 12-month blocks, Part D counts every individual full month you went without coverage.
The formula is 1% of the national base beneficiary premium for each uncovered month, rounded to the nearest 10 cents. The national base beneficiary premium for 2026 is $38.99, so a single uncovered month adds roughly $0.39, and that adds up fast the longer the gap runs: 24 uncovered months works out to roughly $9.36 a month in penalty.
That dollar amount gets added on top of whatever specific Part D plan premium you actually choose, not the national base figure itself, so two people with the identical penalty percentage can end up paying different total premiums depending on which plan they pick.
Like the Part B penalty, this one is permanent. It applies for as long as you have Medicare drug coverage, even if you switch plans later, and it is recalculated every year against that year's national base beneficiary premium.
That means the dollar amount you actually pay tends to drift upward over time even though the number of months you originally went uncovered never changes.
Not every coverage gap counts. If you had creditable prescription drug coverage from another source, commonly a current employer or union health plan, or TRICARE, while you delayed enrolling in Part D, those months typically should not count toward the penalty.
Your plan sends you an annual notice each fall confirming whether your current drug coverage is creditable, keep that notice, since it is the documentation you would need if a penalty is ever applied in error.
The best way to avoid this penalty entirely is enrolling in a Part D plan, or confirming you have other creditable coverage, during your Initial Enrollment Period around when you first become eligible for Medicare, rather than waiting until you actually need prescription coverage.
Frequently asked questions
How is the Part D penalty different from the Part B penalty?
Part B counts full 12-month periods and adds 10% per period to the standard Part B premium. Part D counts every individual full month and adds 1% per month of the national base beneficiary premium, a much smaller unit, but it accumulates monthly instead of yearly.
Is the penalty added to my specific plan's premium or a national average?
It is calculated using the national base beneficiary premium, but the resulting dollar penalty gets added on top of whatever Part D plan premium you actually choose, which can be higher or lower than the national base figure.
What counts as creditable prescription drug coverage?
Coverage that is expected to pay at least as much as standard Medicare drug coverage, commonly a current employer or union plan, or TRICARE. If your prior coverage was creditable, those months should not count toward the penalty.
Does the penalty amount ever change?
Yes. It is recalculated every year against that year's national base beneficiary premium, so the dollar amount typically increases over time even though the number of uncovered months in your history never changes.