Medicare Late-Enrollment Penalty Calculator
The two most-feared Medicare numbers: the Part B late-enrollment penalty (10% of base premium for every full 12 months you delayed) and the Part D late-enrollment penalty (1% of national base premium for every month without creditable coverage). Both attach to your premium for life — the only way to remove them is to die.
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How the formulas work
Part B penalty: 10% of the base Part B premium added for every full 12 months you went without coverage when eligible. Base premium for 2026 is $202.90, so each 12-month delay adds $20.29/month permanently.
Part D penalty: 1% of the national base Part D premium ($36.78 for 2026) for every full month without "creditable" prescription drug coverage. Each year of delay adds 12% × $36.78 = $4.41/month.
"Creditable coverage" exemptions
If you had qualifying coverage during the gap, the months don't count toward the penalty. Common qualifying sources:
- Group employer coverage from a current employer (yours or your spouse's) with 20+ employees
- Federal employee health benefits (FEHB)
- VA healthcare for the Part D penalty (full prescription coverage). VA does NOT exempt the Part B penalty.
- TRICARE for both Part B and Part D in most cases
- COBRA does NOT count. Common, expensive mistake.
- Retiree coverage may or may not count — check the plan's "creditable coverage notice" sent yearly.
Appealing a penalty
The penalty itself is not appealable, but the question of whether you had creditable coverage during a given period is. If CMS imposed a penalty for a gap when you actually had qualifying employer coverage, file Form CMS-L564 with your employer's verification — penalty removed.