Medicare enrollment has strict timing rules — and missing them can mean permanent premium penalties that follow you for life. Here are the windows you need to know.

Initial Enrollment Period (IEP)

Your IEP is a 7-month window centered on your 65th birthday:

  • 3 months before the month you turn 65
  • The month you turn 65
  • 3 months after the month you turn 65

Enrolling in Part B during the first 3 months of your IEP ensures coverage starts on time. Enrolling in the 4 months after your birthday month may delay coverage.

Late enrollment penalties are permanent. If you miss your IEP for Part B without a qualifying reason, you'll pay a 10% premium surcharge for every full 12-month period you went without coverage. This surcharge applies for as long as you have Part B — which is often decades.

Advertisement 468 × 60

Special Enrollment Period (SEP)

If you or your spouse had employer health coverage when you turned 65, you can delay Medicare without penalty and enroll during a Special Enrollment Period when that coverage ends. Your SEP lasts 8 months after coverage ends.

Important: COBRA coverage does not qualify as employer coverage for SEP purposes. Once COBRA begins, your SEP clock may already be running.

Annual Enrollment Period (AEP)

October 15 – December 7 each year. During AEP, you can:

  • Switch between Original Medicare and Medicare Advantage
  • Change your Medicare Advantage or Part D plan
  • Add, drop, or switch a Part D prescription drug plan

General Enrollment Period (GEP)

January 1 – March 31 each year. For seniors who missed their IEP and don't qualify for a SEP, the GEP is the fallback enrollment window. Coverage begins July 1. Late enrollment penalties still apply.

Medicare Advantage Open Enrollment

January 1 – March 31 each year. If you're already in a Medicare Advantage plan, you can switch to another Advantage plan or return to Original Medicare once during this period.