Part D’s Strict 63-Day Window
Part D has a much shorter Special Enrollment Period than Part B. When you lose creditable drug coverage from your employer, you have only 63 days to enroll in a Medicare Part D plan without penalty.
Miss this window and you’ll pay a permanent penalty: 1% of the national base premium for each month you went without creditable drug coverage. The 2026 base premium is approximately $36.00, so even a year delay adds $4.32/month — for life.
What Counts as “Creditable” Drug Coverage?
Drug coverage is creditable if it’s expected to pay, on average, at least as much as Medicare’s standard Part D plan. Most large employer prescription plans qualify, but you need written confirmation.
Each year, your employer must provide a Notice of Creditable Coverage letter. Keep these letters — they’re your proof to Social Security that you don’t owe a Part D penalty.
The 63-Day SEP Clock
Your 63-day window starts the day after your creditable drug coverage ends. Within this window, you can:
- Enroll in a standalone Part D Prescription Drug Plan
- Enroll in a Medicare Advantage plan that includes drug coverage
Don’t Confuse Part B and Part D Windows
Many California workers assume the 8-month Part B window also covers Part D. It does not. Part B SEP is 8 months; Part D creditable coverage SEP is 63 days. If you delay drug coverage even a month past the 63-day window, you start accumulating the lifetime penalty.