Every Medicare enrollment window, one calendar.
Medicare has seven enrollment periods, five acronyms, and one calendar. Miss the wrong one and you pay a penalty for life. Here is every window that matters.
1. Initial Enrollment Period (IEP)
Your first chance to sign up. It spans 7 months: 3 months before your 65th birthday month, your birthday month, and 3 months after. Enroll early and coverage starts on time. Enroll late and you risk gaps and penalties.
| When you enroll | Coverage starts |
|---|---|
| 1–3 months before birthday month | First day of your birthday month |
| Birthday month | Month after your birthday month |
| 1–3 months after birthday month | 2–3 month delay (varies) |
| After IEP ends | Must wait for GEP (Jan–Mar); coverage not until July; penalty applies |
2. Medigap Open Enrollment
This is the most important Medigap window. It lasts 6 months and starts the first month you have Part B and are age 65 or older. During this period, any Medigap insurer must sell you any plan they offer, at any price, regardless of your health conditions. After this window, insurers can deny you coverage or charge more based on your health.
3. Annual Enrollment Period (AEP)
October 15 to December 7 every year. This is when you can change your Medicare Advantage plan, switch back to Original Medicare, or add, drop, or change your Part D drug plan. Changes take effect January 1.
4. Medicare Advantage Open Enrollment (MA-OEP)
January 1 to March 31 each year. If you are in a Medicare Advantage plan, you can switch to a different Advantage plan or return to Original Medicare during this window. You cannot add a new Part D plan if you return to Original Medicare during MA-OEP — you would need to do that during AEP.
5. General Enrollment Period (GEP)
January 1 to March 31 each year. This is the catch-up window for people who missed their IEP. If you enroll during GEP, coverage starts July 1, and you may owe a late enrollment penalty on your Part B premium.
6. Special Enrollment Periods (SEPs)
SEPs open when life events happen: losing employer coverage, moving out of your plan's service area, qualifying for Medicaid, or other qualifying circumstances. Each SEP has its own rules and timeframes.
The two penalties to respect
Late enrollment penalties are not one-time fees. They are added to your premium for as long as you have Medicare.
| Penalty | How it works | Duration |
|---|---|---|
| Part B late enrollment | +10% premium for every 12-month period you were eligible but did not enroll | Lifetime |
| Part D late enrollment | +1% premium per month for every month without creditable drug coverage | Lifetime |
Professor's Note: Mark these dates on your calendar the moment you turn 64. A 15-minute planning session now can save you thousands in penalties and months of coverage gaps later. That is not an exaggeration — we see it every year.
Questions from this lesson
What happens if I miss my Initial Enrollment Period?
You may face a lifetime late enrollment penalty on your Part B premium (10% for every 12-month period you were eligible but did not enroll). You would also have to wait for the General Enrollment Period (Jan 1 – Mar 31) to enroll, with coverage not starting until July.
Can I change my Medicare Advantage plan outside of AEP?
Yes. The Medicare Advantage Open Enrollment Period (MA-OEP) runs January 1 to March 31, and allows you to switch to a different Advantage plan or return to Original Medicare. You cannot add a Medigap plan during this window.
What is a Special Enrollment Period?
A Special Enrollment Period (SEP) opens when you experience certain life events, such as losing employer coverage, moving out of your plan's service area, or qualifying for Medicaid. SEPs give you a limited time to make changes outside the standard enrollment windows.
When should I enroll in Medigap?
The best time is during your 6-month Medigap Open Enrollment Period, which starts the first month you have Part B and you are 65+. During this window, insurers cannot deny you coverage or charge more due to health conditions. Missing this window may mean health underwriting and higher premiums.
Not sure which window you are in?
We will look at your situation and tell you exactly which deadlines apply — and which ones to ignore.