The Complete Guide to Medicare Enrollment Deadlines (Initial, SEP, AEP) — What to Do If You Missed One
Medicare enrollment can feel straightforward until you realize there are multiple “windows” with different rules—especially if you’re turning 65 soon or you’ve lost employer coverage. Missing the wrong deadline can mean coverage gaps and, in some cases, late-enrollment penalties.
This guide breaks down the big three enrollment periods people ask about most—Initial Enrollment Period (IEP), Special Enrollment Periods (SEP), and Annual Enrollment Period (AEP)—with real-world scenarios and a simple timeline so you can act confidently.
Note: People sometimes say “Medicare Open Enrollment starts January 1.” What starts January 1 is Medicare Advantage Open Enrollment (Jan 1–Mar 31) for people already enrolled in a Medicare Advantage plan, and the General Enrollment Period (Jan 1–Mar 31) for people who missed certain Part A/Part B deadlines. It is not the main Fall Medicare Open Enrollment (AEP), which runs Oct 15–Dec 7.
1) Initial Enrollment Period (IEP) — Turning 65
When it happens: A 7-month window
3 months before the month you turn 65
Your birthday month
3 months after your birthday month
Who it’s for:
People becoming eligible because they’re turning 65 (and some who qualify due to disability)
Why it matters:
This is your “first chance” to enroll in Original Medicare (Part A and/or Part B) and decide whether you’ll add:
A Medicare Advantage plan (Part C), and/or
A Part D prescription drug plan
2) Special Enrollment Period (SEP) — Life Events (Often Employer Coverage Changes)
What triggers it: Specific life events, like losing other coverage, moving, etc. The timing and what you can change depends on the event. Medicare
Common high-impact SEP (working past 65):
If you delayed Part B because you had job-based coverage, you typically have an 8-month SEP to enroll in Part B when you stop working or lose the employer coverage—even if you elect COBRA after the job ends.
3) Annual Enrollment Period (AEP) — Fall “Medicare Open Enrollment”
When it happens: October 15 to December 7 every year
Who it’s for: People who already have Medicare and want to change plan choices for next year.
What you can do: (Common examples)
Switch Medicare Advantage plans
Move between Original Medicare and Medicare Advantage
Join, drop, or change a Part D drug plan
Changes typically take effect January 1 (as long as the plan receives your request by Dec 7).
4) If You Missed IEP/SEP: General Enrollment Period (GEP)
When it happens: January 1 to March 31
What it’s for: A chance to enroll in Part A and/or Part B if you didn’t enroll during IEP and don’t qualify for an SEP.
Coverage start: Coverage generally starts the month after you sign up.
5) January 1–March 31: Medicare Advantage Open Enrollment (MA OEP)
When it happens: January 1 to March 31
Who it’s for: Only people currently enrolled in a Medicare Advantage plan.
What you can do (one-time change):
Switch to another Medicare Advantage plan, or
Drop Medicare Advantage and return to Original Medicare (and you can add a Part D plan)
Real-World Scenarios (What to Do)
Scenario A: “I’m turning 65 soon. What should I do first?”
Identify your IEP window (the 7-month timeline around your birthday).
Decide whether you’re enrolling in Original Medicare (A & B), and then whether you want:
Medicare Advantage (Part C), or
Original Medicare + Part D, and potentially a Medigap plan (depending on your situation and timing).
Enroll early if possible to avoid last-minute issues and reduce the chance of a coverage gap.
Scenario B: “I’m 65+ and I’m losing employer coverage.”
If you had job-based coverage and delayed Part B, you may have an 8-month SEP to enroll in Part B after you stop working or lose the coverage (even if you choose COBRA).
This is one of the most important timelines to get right—because missing it can push you into the General Enrollment Period and potential penalties.
Scenario C: “I missed my IEP (or didn’t realize I needed Part B).”
Your options depend on whether you qualify for an SEP. If not, you may need to use the General Enrollment Period (Jan 1–Mar 31) to enroll in Part A/Part B, and coverage generally begins the month after enrollment.
Scenario D: “I missed AEP (Oct 15–Dec 7). Am I stuck all year?”
Not necessarily.
If you qualify for a Special Enrollment Period, you may be able to change coverage outside AEP due to a life event.
If you’re already enrolled in Medicare Advantage, you may still have a one-time switch opportunity during Jan 1–Mar 31 (MA OEP).
FAQ: Medicare Enrollment Deadlines
What are the main Medicare enrollment deadlines I should remember?
IEP: 7-month window around turning 65
AEP: Oct 15–Dec 7
MA OEP: Jan 1–Mar 31 (if you’re already on Medicare Advantage)
GEP: Jan 1–Mar 31 (for Part A/B if you missed IEP/SEP)
If I’m still working at 65, can I delay Medicare?
Many people can delay Part B if they have qualifying job-based coverage, but the rules depend on your exact situation. Once you stop working or lose employer coverage, you typically have an 8-month SEP to enroll in Part B (and that SEP begins when work/coverage ends—even if COBRA is elected).
What if I missed Medicare enrollment and need coverage now?
Start by checking whether you qualify for an SEP (life events, loss of coverage, relocation, etc.). If you don’t, the General Enrollment Period (Jan 1–Mar 31) may be your path to Part A/Part B enrollment, with coverage generally starting the month after you enroll.
What does “Medicare Open Enrollment” mean?
It’s often used to mean AEP (Oct 15–Dec 7), when people can change Medicare Advantage and Part D plans for the next year.
However, some people use the phrase to refer to January–March periods (MA OEP or GEP), which are different and more limited.
Quick Checklist: “Schedule an Enrollment Check” (CTA)
If you’re:
Turning 65 in the next 3–6 months
Losing employer coverage (or considering COBRA)
Confused about whether you qualify for an SEP
Unsure if your current Medicare plan still fits your prescriptions and doctors
…schedule a quick Medicare enrollment check with our local team.
Jackson Insurance Group
London, KY and surrounding areas
(606) 249-6880 | support@jigky.com | jigky.com
Not affiliated with or endorsed by Medicare or any government agency. Enrollment periods and eligibility rules are subject to specific conditions; we’ll confirm your options based on your situation.