Medicare enrollment windows at a glance
Here's how to find your enrollment window.
The IEP-vs-AEP confusion is the most expensive mistake in Medicare. Here's the order I'd take.
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Identify which enrollment window applies to your situation
Are you turning 65 soon and not yet enrolled? You need IEP. Did you miss IEP without qualifying coverage? You need GEP. Are you losing employer coverage? You need SEP. Already enrolled and want to switch a Medicare Advantage or Part D plan? You need AEP or MA OEP.
Picking the wrong window doesn't enroll you in anything — and may extend the time you're paying late penalties. Get this right first.
Time: 5 minutes to think through Cost: Free
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Find your IEP — the 7-month window around your 65th birthday
Your IEP is the 3 months before your 65th birthday month, your birthday month, and the 3 months after. Sign up in the 3 months BEFORE your birthday month — coverage starts on the first of your birthday month.
Wait until your birthday month or after and coverage starts later. The earlier in IEP you enroll, the cleaner the start date.
Time: 5 minutes Cost: Free Find when Medicare coverage starts ›
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If you missed IEP, plan for GEP or SEP
If you missed IEP without qualifying employer coverage, the General Enrollment Period (GEP) runs January 1–March 31 each year, with coverage starting the month after enrollment. The Part B late-enrollment penalty applies and is permanent.
If you had qualifying employer coverage and it's now ending, you have an 8-month Special Enrollment Period (SEP) starting from the month coverage ends or the month employment ends, whichever is earlier. SEP avoids the late-enrollment penalty. Document the end date carefully.
Time: 10 minutes Cost: Free
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Don't confuse AEP (switch plans) with IEP (first enroll) — they do different things
Annual Enrollment Period (Oct 15–Dec 7) is for switching Medicare Advantage or Part D plans — NOT for first-time enrollment in Original Medicare. If you've never enrolled in Medicare and you sign up only during AEP for a Medicare Advantage plan, you may have already triggered late-enrollment penalties from missing IEP.
If you're not sure which window applies to you, ask a SHIP counselor at 1-877-839-2675 or Chapter Medicare at (352) 841-0632 before you enroll in anything. They can tell you in 10 minutes which window you actually need.
Time: 10 minutes to confirm Cost: Free Free Medicare help ›
Which of these fits your situation?
Each Medicare enrollment window has a different purpose. Pick the one that fits.
I'm approaching 65 — when do I sign up?Use your IEP — the 7-month window around your 65th birthday
Sign up during your Initial Enrollment Period — the 7-month window that starts 3 months before your 65th birthday month, includes your birthday month, and runs 3 months after.
For the cleanest start, enroll in the first 3 months of IEP. Coverage then begins on the first of your birthday month. If you wait until your birthday month or later, coverage starts later — in some cases, the month after you enroll.
I'm working past 65 with employer coverage — when does my SEP start?Your SEP starts when employment OR coverage ends — whichever is earlier
If you (or your spouse) have group health insurance through current active employment with 20+ employees, your 8-month Special Enrollment Period starts the month your employment ends OR the month your group coverage ends — whichever is earlier.
Most people enroll in Part A at 65 even when delaying Part B — it's premium-free if you have 40 work credits. (HSA contributors should pause and check first — Medicare enrollment ends HSA contributions.)
I missed my IEP — what now?Use the General Enrollment Period (Jan 1 – Mar 31)
If you missed IEP without qualifying employer coverage, the General Enrollment Period (GEP) runs January 1–March 31 each year. Coverage starts the month after enrollment under the rules updated in 2023.
The Part B late-enrollment penalty is 10% added to your premium for every full 12 months you were eligible but did not enroll — permanent for life. If you delayed 3 years past your IEP, your Part B premium is 30% higher for life.
I want to switch from Original Medicare to Medicare Advantage (or vice versa)Use AEP (Oct 15 – Dec 7) for the change — watch the underwriting trap
The Annual Enrollment Period (October 15–December 7) is when you can switch between Original Medicare and Medicare Advantage, change Medicare Advantage plans, or join/drop a Part D drug plan. Changes take effect January 1.
The trap: if you switch from Medicare Advantage back to Original Medicare and want to add a Medigap supplement, Medigap insurers in most states can require medical underwriting and can deny you based on health. Your one-time guaranteed-issue Medigap right is during the 6-month Medigap Open Enrollment Period that starts when you first enroll in Part B at 65.
I'm already on Medicare Advantage but want to change — when can I do that?Use Medicare Advantage Open Enrollment (Jan 1 – Mar 31)
If you're already enrolled in Medicare Advantage as of January 1, the Medicare Advantage Open Enrollment Period (MA OEP) runs January 1–March 31. You can use MA OEP to switch to a different MA plan once or to drop MA and return to Original Medicare (with or without a Part D plan).
You can only make one change during MA OEP. The change takes effect the first of the month after the plan receives the request. The same Medigap underwriting risk applies if you go back to Original Medicare and want a Medigap supplement.
I just moved to a new state — does that open an SEP?Yes — if your move puts you outside your current plan's service area
Moving outside your Medicare Advantage or Part D plan's service area triggers a Special Enrollment Period to switch plans. You typically have 2 months from the month after the move (or the month after you tell your plan, if later) to enroll in a new plan.
Several other moves also trigger SEPs: moving back to the U.S. from abroad, moving in or out of a nursing home, and gaining or losing Medicaid eligibility. Document the date carefully so you can prove the SEP if asked.
I'm helping a parent navigate Medicare enrollment timingBystander — I'm not the one enrolling
If you're helping a parent figure out which Medicare window to use, the most important thing is to identify whether they have qualifying active employer coverage. If yes, an 8-month SEP applies when that coverage ends. If no, they need to enroll during the 7-month IEP around their 65th birthday or face a permanent Part B penalty.
Form SSA-1696 lets you act as their authorized representative on the SSA side. With that on file, you can call SSA on their behalf, discuss their case, and assist with enrollment. SHIP at 1-877-839-2675 can help you both walk through the timing decision for free.
My situation is different from theseTell me what's specific to you
There are a half-dozen rarer SEPs that don't fit standard scripts: 5-Star plan SEP (switch to a 5-star plan once a year), exceptional-condition SEPs (CMS uses these for emergencies and disasters), Extra Help/LIS quarterly SEPs, and SEPs tied to leaving Medicaid or losing employer coverage in non-standard ways.
For anything outside the standard windows, a free SHIP call at 1-877-839-2675 or Chapter Medicare at (352) 841-0632 is faster than guessing.
Medicare enrollment questions I get most often
What's the IEP and when does it start?
The Initial Enrollment Period (IEP) is the 7-month window centered on your 65th birthday: 3 months before your birthday month, your birthday month, and 3 months after.
If your birthday is on the 1st of a month, your IEP shifts back by one month — it starts 4 months before your actual birthday month rather than 3.
What's the difference between SEP and GEP?
Special Enrollment Period (SEP) opens because of a qualifying life event — most commonly losing employer coverage. SEP avoids the late-enrollment penalty.
General Enrollment Period (GEP) is the once-a-year backup window (Jan 1–Mar 31) for people who missed IEP without an SEP. The Part B late-enrollment penalty applies and is permanent.
Can I enroll in Medicare anytime during the year?
No — Medicare enrollment is window-based. You can only enroll during a specific window: IEP (the first time at 65), GEP (Jan 1–Mar 31 each year), an SEP (when a qualifying event occurs), or AEP/MA OEP (for switching plans).
Trying to enroll outside a valid window doesn't work — SSA will tell you to come back during the next available window. Plan ahead.
When does my Medicare coverage actually start after I sign up?
If you enroll during the first 3 months of IEP, coverage starts the first of your 65th birthday month. If you enroll during your birthday month or the 3 months after, coverage starts the first of the month after you enroll.
For GEP enrollments (Jan 1–Mar 31), coverage starts the first of the month after enrollment under rules updated effective 2023. For SEP enrollments, coverage usually starts the month after enrollment but can sometimes start the month of enrollment if you ask.
What's the difference between AEP and Medicare Advantage Open Enrollment?
Annual Enrollment Period (AEP, Oct 15–Dec 7) is broader: anyone with Medicare can switch between Original Medicare and Medicare Advantage, change Medicare Advantage plans, or join/drop a Part D drug plan.
Medicare Advantage Open Enrollment Period (MA OEP, Jan 1–Mar 31) is narrower: only people already enrolled in a Medicare Advantage plan can use it, and only for one change — either switch to a different MA plan or go back to Original Medicare.
I missed every window — am I stuck without Medicare?
No — the General Enrollment Period (Jan 1–Mar 31) is always the backup. You can always enroll during GEP, with coverage starting the month after enrollment.
The cost of missing windows is the late-enrollment penalty, not denial. You won't be locked out of Medicare entirely; you'll pay a permanent premium surcharge until something gets you off the Part B rolls.
Does losing Medicaid trigger a Medicare SEP?
Yes. If you lose Medicaid coverage — for example, after a state Medicaid renewal redetermination — you typically get an SEP to enroll in or switch a Medicare Advantage or Part D plan.
The SEP rules around Medicaid loss expanded in 2023–2024 in connection with the post-pandemic Medicaid unwinding. Document the Medicaid termination notice and apply quickly. SHIP at 1-877-839-2675 can help.
Can I delay Part D and avoid the penalty?
Only if you have creditable prescription drug coverage from another source — typically employer or union retiree drug coverage that the plan certifies as creditable (at least as good as standard Medicare Part D).
If you don't have creditable drug coverage and you delay Part D, the Part D late-enrollment penalty is 1% of the national base beneficiary premium ($38.99/mo in 2026) for every full month you went without creditable coverage — added to your Part D premium permanently.
Are there 5-Star SEPs for switching plans outside AEP?
Yes — the 5-Star SEP runs December 8 through November 30 each year. If a Medicare Advantage plan, Part D plan, or Medicare Cost plan in your area has earned a 5-star quality rating from CMS, you can switch into it once during this window outside the normal AEP/MA OEP.
Not all areas have 5-star plans available. Check medicare.gov's plan finder to see which plans (if any) in your area are 5-star.
How do I appeal if SSA denied my Special Enrollment Period?
If SSA denied your SEP request, you can ask for reconsideration by submitting documentation of the qualifying event (e.g., letter showing employer coverage end date, certificate of creditable coverage). If reconsideration is also denied, you can request an Administrative Law Judge (ALJ) hearing.
The key is documenting the timeline. Save HR letters, COBRA election notices, plan termination letters, and date-stamped emails. SHIP at 1-877-839-2675 can help you build the appeal package for free.
Enrollment is one piece. There are programs that work alongside.
Other programs that interact with your Medicare enrollment timing.
Medicare basics (Hub)
If enrollment timing isn't your only question, the Medicare hub walks through how the four parts work together and what the major decisions look like.
Medicare for SSDI under 65
If you're getting Medicare under 65 because of SSDI, the timing is automatic — 24 months after your first SSDI cash check. ALS waives the wait. ESRD has its own rules.
Late-enrollment penalty (Part B)
If you missed IEP without an SEP, the Part B late-enrollment penalty is 10% per year, permanently. The longer you delay, the bigger the permanent surcharge.
Working past 65 with employer coverage
If you're still working at 65 with active employer coverage from a 20+ employee employer, you can usually delay Part B safely. Smaller employers and COBRA do not count the same way.
Medicare and Social Security at 65
If you're delaying Social Security past 65, Medicare doesn't enroll automatically — you have to apply yourself. This is the single most expensive Medicare timing mistake.
Annual Enrollment Period (AEP)
AEP (Oct 15 – Dec 7) is for changing Medicare Advantage or Part D plans — not for first-time Medicare enrollment. Different window, different purpose.
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