AEP vs OEP Medicare Enrollment: Understanding the Difference and What It Means Operationally

Medicare has two primary enrollment windows. Most people know about one. Many confuse the two. And health plans that don’t manage both correctly create member experience failures, compliance risk, and missed retention opportunities.

The Annual Enrollment Period and the Medicare Advantage Open Enrollment Period are not the same thing. They run at different times, serve different populations, and allow different plan changes. And they require different operational responses from health plans, member services teams, and the contact centers supporting them.

This guide covers everything you need to know about AEP vs OEP Medicare enrollment — the dates, the rules, who’s eligible, what they can do, and what health plans need to do operationally during each period.

AEP vs OEP — The Quick Comparison

Feature	AEP — Annual Enrollment Period	OEP — Open Enrollment Period
Dates	October 15 – December 7	January 1 – March 31
Coverage effective	January 1 of the following year	First day of the month following enrollment
Who can use it	All Medicare beneficiaries	Only current Medicare Advantage enrollees
What they can do	Switch MA plans; join/drop MA; join/drop Part D; switch Part D plans	Switch from one MA plan to another; drop MA and return to Original Medicare
Can join a new MA plan?	Yes — if not already enrolled in MA	No — only existing MA members can use OEP
Can add standalone Part D?	Yes	Only if dropping MA-PD and returning to Original Medicare
Number of changes allowed	Unlimited — last change before December 7 is what counts	One change total — OEP cannot be used again after first change
Outbound marketing by plans	Permitted — subject to CMS marketing guidelines	Prohibited — plans cannot market to members during OEP

The Annual Enrollment Period — Full Details

What AEP Is

AEP runs from October 15 through December 7 every year. It is the main Medicare enrollment window. Every Medicare beneficiary can use it — whether they have Original Medicare, Medicare Advantage, or a standalone Part D plan.

AEP is when health plans compete most intensely for members. Benefits packages for the next plan year take effect January 1. Members receive their Annual Notice of Change in late September. They read it, compare their options, and decide whether to stay or switch. The decisions they make during these 53 days determine plan membership — and plan revenue — for the entire coming year.

What Beneficiaries Can Do During AEP

• Switch from one Medicare Advantage plan to another
• Join a Medicare Advantage plan for the first time (if currently on Original Medicare)
• Drop Medicare Advantage and return to Original Medicare
• Join a standalone Medicare Part D prescription drug plan
• Switch from one Part D plan to another
• Drop Part D coverage entirely

There is no limit on how many times a beneficiary can change their mind during AEP. Whatever plan they’re enrolled in on December 7 is the plan that takes effect January 1. A member who switched three times has coverage through the plan they last selected.

What Plans Must Do During AEP

AEP is operationally demanding. Volume spikes 3–5× above steady state. Agents must know the next year’s benefit structure precisely. CMS marketing compliance governs every outbound contact. And the retention stakes are enormous — every member who leaves during AEP takes their premium revenue for the entire coming year.

The full AEP preparation framework — staffing timelines, training requirements, compliance certification, quality monitoring — is in our open enrollment call center preparation guide.

Key AEP operational requirements:

• All agents trained and CMS compliance certified before October 15
• 2027 benefit curriculum delivered, tested, and quality-validated pre-launch
• AEP surge capacity in place — staffed to week-one volume, not average AEP volume
• Proactive retention outreach to at-risk members beginning week one
• 100% quality monitoring is active from October 15
• Multilingual coverage for Spanish-speaking and other LEP member populations

The Medicare Advantage Open Enrollment Period — Full Details

What OEP Is

OEP runs January 1 through March 31 every year. It was created by the Medicare Access and CHIP Reauthorization Act of 2015 to give Medicare Advantage members a limited second chance to make changes after AEP if they enrolled in the wrong plan or if their circumstances changed.

OEP is not a second AEP. It is narrower in scope, more restricted in what changes it allows, and — critically — governed by a strict prohibition on plan marketing activity.

Who Can Use OEP

Only current Medicare Advantage enrollees can use OEP. A beneficiary on Original Medicare cannot use OEP to join a Medicare Advantage plan for the first time. If they want to join MA, they need to wait for AEP — or qualify for a Special Enrollment Period.

This is one of the most common misconceptions among members. Beneficiaries who missed AEP and want to join Medicare Advantage frequently call member services in January or February, thinking OEP is their window. It isn’t — not for new MA enrollment.

What OEP Allows

Current MA enrollees have two options during OEP:

Option 1: Switch from their current MA plan to a different MA plan. The new plan’s coverage begins the first day of the month following enrollment. A member who switches in February has new coverage on March 1.

Option 2: Drop their MA plan entirely and return to Original Medicare. If the MA plan included Part D drug coverage (MA-PD), they can also enroll in a standalone Part D plan when returning to Original Medicare.

That’s it. No other changes are permitted during OEP.

The One-Change Rule

OEP is a one-and-done window. Once a Medicare Advantage member makes a change during OEP — any change — they cannot make another change through OEP. The single-change rule is strict. A member who switches MA plans in January cannot switch again in February using OEP.

This is the second most common member misconception. Members who switched in January sometimes call in February wanting to switch again. They believe OEP gives them the same flexibility as AEP. It doesn’t.

The OEP Marketing Prohibition

CMS prohibits plans from marketing to current enrollees during OEP. This means no outbound retention calls targeting current members. No mailers promoting plan benefits. No advertising campaigns aimed at persuading current members to stay or switch. The prohibition applies to plans targeting their own members as well as competitors targeting other plans’ members.

Members can call their plan during OEP and ask questions. They can initiate a plan switch. Plans can respond to inbound inquiries. What plans cannot do is proactively solicit OEP activity.

The marketing prohibition is one of the most compliance-sensitive areas in Medicare plan operations. A single documented outbound OEP marketing contact can trigger a CMS investigation. Every agent handling OEP contacts must understand exactly where the line is — responding to inbound inquiries vs. soliciting plan changes.

Beyond AEP and OEP — Other Medicare Enrollment Periods

AEP and OEP are the two regularly scheduled enrollment windows. But Medicare has several other enrollment periods that member services agents must know — because members call about them throughout the year.

Initial Enrollment Period (IEP)

New Medicare beneficiaries get a 7-month window to enroll — the 3 months before their 65th birthday month, their birthday month, and the 3 months after. Missing an IEP without qualifying for an exception results in lifetime late-enrollment penalties for Part B and Part D.

IEP contacts are emotionally significant. Many are from people navigating Medicare for the first time. They’re confused. They’re worried about penalties. They have genuine decisions to make about Original Medicare vs. Medicare Advantage, Medigap, and Part D. Agents handling IEP contacts need patience, depth of plan knowledge, and genuine benefit-navigation ability — not a script.

Special Enrollment Periods (SEPs)

SEPs allow Medicare beneficiaries to enroll or make changes outside of standard enrollment windows when specific qualifying life events occur. There are over a dozen defined SEPs. The most common are:

• Loss of employer coverage SEP — when a beneficiary or their spouse loses employer-sponsored health coverage
• Moving SEP — when a member moves out of their plan’s service area
• Plan termination SEP — when a beneficiary’s plan exits the market
• Low-income subsidy SEP — available monthly to members who receive Extra Help or Medicaid
• Five-star SEP — allows a one-time switch to a 5-star plan between December 8 and November 30
• ICEP (Initial Coverage Election Period) — for newly eligible beneficiaries joining MA for the first time

SEPs are one of the most compliance-sensitive areas in Medicare enrollment. Enrolling a member under an SEP they don’t actually qualify for is a CMS violation. Agents must verify SEP eligibility before processing any enrollment, not assume eligibility based on the member’s self-report.

General Enrollment Period (GEP)

The GEP runs January 1 through March 31 — the same dates as OEP, which creates frequent member confusion. The GEP is specifically for beneficiaries who missed their IEP for Part A and/or Part B. Coverage begins July 1. Late enrollment penalties may apply. The GEP is not a window for Medicare Advantage enrollment — that’s what OEP is for, and OEP is only available to current MA members.

Enrollment Period	When	Who	What They Can Do
AEP	Oct 15 – Dec 7	All Medicare beneficiaries	Switch/join/drop MA; switch/join/drop Part D
OEP	Jan 1 – Mar 31	Current MA enrollees only	Switch MA plans; drop MA (one change only)
IEP	3 months before/after 65th birthday month (7 months total)	New Medicare beneficiaries	Enroll in Part A, B, MA, and/or Part D for first time
GEP	Jan 1 – Mar 31	Those who missed IEP for Part A/B	Enroll in Part A/B (coverage July 1; penalties may apply)
SEP	Varies by qualifying event	Beneficiaries with qualifying life events	Varies by SEP type — agent must verify eligibility

Common AEP and OEP Member Misconceptions — What Member Services Must Address

These are the misconceptions that generate the most confusion among members and the highest compliance risk in Medicare member services. Every agent needs to address them correctly — every time.

“I missed AEP. Can I still change my plan?”

Answer: It depends. If the member is currently in a Medicare Advantage plan, they may be able to use OEP (January 1–March 31) to switch to another MA plan or return to Original Medicare. If they want to join MA for the first time or make a different kind of change, they’ll need a qualifying SEP or will have to wait for next AEP.

The wrong answer — “yes, OEP lets you change your plan” without clarifying who OEP applies to — sets up the misconception that OEP is available to everyone. It isn’t.

“Can I switch plans twice using OEP?”

Answer: No. OEP allows one change. Once the member makes a change during OEP, they cannot make another through OEP. A second change during January 1–March 31 would require a qualifying SEP.

“My neighbor told me I can join a Medicare Advantage plan in February.”

Answer: Only if the member is currently in a Medicare Advantage plan and hasn’t already used their OEP change. If they’re on Original Medicare and missed AEP, they cannot join a Medicare Advantage plan during OEP. They need a qualifying SEP or must wait for the next AEP.

“I want to add dental coverage to my plan during OEP.”

Answer: If a member wants to add supplemental benefits that aren’t currently in their plan, their option during OEP is to switch to a different MA plan that includes those benefits. OEP itself doesn’t allow adding benefits to an existing plan — it only allows plan changes.

“My plan’s benefits changed. Can I switch during OEP because of that?”

Answer: Yes — benefit changes are not a requirement to use OEP, but any current MA member can use OEP to switch plans regardless of why. They don’t need to cite a reason. The OEP window is available from January 1–March 31 to all current MA enrollees for one change.

What Health Plans Must Do Differently During AEP vs. OEP

AEP and OEP require entirely different operational postures. The same member services team handles both — but the rules, the compliance requirements, and the member communication standards change significantly between the two windows.

During AEP (October 15 – December 7)

AEP is an active, high-volume, outbound and inbound period. Plans proactively retain members, acquire new ones, and compete aggressively — within CMS marketing guidelines. The operational requirements are significant:

• Agents must know the next year’s benefit structure for every plan supported — accurately and specifically
• All outbound retention contacts must comply with CMS AEP marketing guidelines
• Agents must not steer members toward specific plans using non-approved language
• Every contact must include required disclosures — agent name, plan name, CMS disclaimer
• Recording requirements apply to all AEP contacts
• Volume surges require pre-planned surge capacity — starting in August

During OEP (January 1 – March 31)

OEP is a passive, inbound-response period. Plans cannot proactively solicit changes to members. They respond to member-initiated contacts. The operational requirements are different — and the compliance pitfalls are distinct:

• No outbound marketing to current members — including retention calls that pitch plan benefits
• Agents may respond to inbound inquiries and assist with member-initiated changes
• Agents must verify OEP eligibility — only current MA members qualify; Original Medicare beneficiaries do not
• Agents must communicate the one-change rule accurately — members cannot make multiple changes through OEP
• Agents must not misrepresent the OEP scope — it does not allow the same changes as AEP

OEP compliance failures tend to be subtler than AEP compliance failures. An agent who proactively calls a member in February “just to check in and make sure you’re happy with your plan” — when that call is actually a soft retention contact — may have crossed the OEP marketing prohibition line. The line between service and solicitation during OEP must be explicitly trained and quality-monitored.

AEP Vs. OEP, and Stars Performance

Both enrollment periods affect Stars ratings through different mechanisms.

AEP drives Stars’ performance through the CAHPS member experience surveys that follow it. Members who have poor AEP experiences — long hold times, inaccurate benefit information, and difficult enrollment processes — report them in CAHPS surveys. Those reports move C15, C16, and C17 scores. Those scores affect the Stars’ ratings. Those ratings affect quality bonus revenue.

OEP affects Stars through disenrollment. Members who used OEP to leave a plan were not retained at AEP — either because the plan’s AEP retention program failed, or because the plan’s year-round member experience drove them to switch. High OEP disenrollment is a lagging indicator of failures in AEP and year-round member experience.

Plans that manage AEP and OEP well — with excellent member services, proactive retention, and compliance-clean operations — typically see lower OEP disenrollment and higher post-AEP CAHPS scores than those that don’t. The operational investment in both periods pays back in Stars performance and quality bonus revenue throughout the following plan year.

The full AEP CAHPS and Stars connection is covered in our Medicare customer support and member retention guide. The AEP preparation framework — covering staffing, training, compliance certification, and quality monitoring — is in our open enrollment call center preparation guide.

Quick Reference — AEP and OEP Compliance Rules for Member Services Agents

Scenario	AEP	OEP
Member on Original Medicare wants to join MA	✅ Eligible — can enroll in MA	❌ Not eligible — OEP is MA members only
Current MA member wants to switch plans	✅ Eligible	✅ Eligible — one change allowed
Current MA member already used OEP change — wants to switch again	N/A — AEP not active	❌ Not eligible — one-change rule exhausted
Member wants to add a standalone Part D	✅ Eligible	Only if dropping MA-PD and returning to Original Medicare
Plan calls member proactively to discuss plan options	✅ Permitted — CMS marketing guidelines apply	❌ Prohibited — OEP marketing ban applies
Member calls plan inbound — agent discusses plan options	✅ Permitted — respond to member inquiry	✅ Permitted — respond to member-initiated inquiry
Coverage effective date	January 1 of the following year	First day of the month following enrollment