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
Frequently Asked Questions
How do I actually sign up for Medicare?+
If you are already receiving Social Security benefits, you are automatically enrolled in Parts A and B when you turn 65. If you are not receiving Social Security, you need to actively sign up. You can enroll online at SSA.gov, by calling Social Security at 1-800-772-1213, or by visiting your local Social Security office. To join a Medicare Advantage or Part D plan, you enroll directly through the private insurer or at Medicare.gov.
Can I enroll in Medicare if I am still working at 65?+
Yes, but your situation depends on your employer. If you work for a company with 20 or more employees, your employer plan is primary and you can delay Part B without penalty. If your employer has fewer than 20 employees, Medicare is primary and you should enroll in Part B on time. Always check with your HR department and verify whether your employer coverage is considered primary before deciding to delay.
What if I missed my Initial Enrollment Period?+
If you missed your IEP without a qualifying reason, you will need to wait for the General Enrollment Period (Jan 1 to Mar 31), with coverage starting July 1. You will also owe a late enrollment penalty on your Part B premium for as long as you have Medicare. If you had employer coverage that has now ended, you likely qualify for a Special Enrollment Period and can avoid the penalty.
Do I need to enroll in Part D separately?+
If you want standalone Part D coverage, yes. You enroll through a private insurer, not through Social Security. If you choose Medicare Advantage, your plan usually includes Part D, so no separate enrollment is needed. If you have employer drug coverage that is creditable, you can delay Part D without penalty until that coverage ends.
When can I switch from Medicare Advantage back to Original Medicare?+
During the Annual Enrollment Period (Oct 15 to Dec 7) you can drop Medicare Advantage and return to Original Medicare. You can also do this during the Medicare Advantage Open Enrollment Period (Jan 1 to Mar 31). Keep in mind that if you want to add a Medigap policy after returning to Original Medicare, you may face medical underwriting in most states unless you have a guaranteed issue right.
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 |