Medicare Enrollment Periods
Last reviewed: June 2026 · Reviewed by Galit Sacajiu MD, MPH
Medicare has strict enrollment windows. Signing up outside your enrollment period — or missing it altogether — can result in permanent premium penalties and gaps in coverage. Understanding when you can enroll is one of the most important steps in managing your Medicare.
Initial Enrollment Period (IEP)
📅 7-month window around your 65th birthday
3 months before the month you turn 65, the month you turn 65, and 3 months after.
Who qualifies
Everyone turning 65 (or gaining Medicare eligibility)
What you can do
- ✓ Enroll in Part A
- ✓ Enroll in Part B
- ✓ Enroll in Part D
- ✓ Join a Medicare Advantage plan
⚠️ Missing this window without qualifying coverage leads to permanent late enrollment penalties.
Annual Enrollment Period (AEP) — Open Enrollment
📅 October 15 – December 7 every year
Changes take effect January 1 of the following year.
Who qualifies
Anyone already enrolled in Medicare
What you can do
- ✓ Switch Medicare Advantage plans
- ✓ Switch Part D plans
- ✓ Move from Medicare Advantage to Original Medicare
- ✓ Move from Original Medicare to Medicare Advantage
Medicare Advantage Open Enrollment Period (MA OEP)
📅 January 1 – March 31 every year
One change allowed. New coverage begins the first day of the following month.
Who qualifies
People enrolled in a Medicare Advantage plan
What you can do
- ✓ Switch to a different Medicare Advantage plan
- ✓ Return to Original Medicare (and join a Part D plan)
⚠️ Cannot switch from Original Medicare to Advantage during this period.
General Enrollment Period (GEP)
📅 January 1 – March 31 every year
Coverage begins July 1. You may owe a late enrollment penalty.
Who qualifies
People who missed their IEP and don't qualify for an SEP
What you can do
- ✓ Enroll in Part A (if not already enrolled)
- ✓ Enroll in Part B
⚠️ Late enrollment penalties apply if you go without creditable coverage.
Special Enrollment Period (SEP)
📅 Triggered by qualifying life events
Timing varies by qualifying event. Usually 8 months after losing employer coverage.
Who qualifies
People with qualifying circumstances
What you can do
- ✓ Enroll in Part B after losing employer coverage
- ✓ Join/switch Medicare Advantage or Part D plans
- ✓ Available for moves, loss of Medicaid, natural disasters, and more
Late Enrollment Penalties
| Part | Penalty | Duration |
|---|---|---|
| Part A | 10% higher premium | 2x the number of years you were eligible but didn't enroll |
| Part B | 10% per 12-month period without coverage | Permanent — for as long as you have Part B |
| Part D | 1% of national base premium per month without creditable coverage | Permanent — added to your monthly premium |