Core Insurance Solutions
    By Core Insurance SolutionsOctober 15, 2026
    Medicare AEP vs OEP: One OEP Change, Exact Dates

    Medicare AEP vs OEP: One OEP Change, Exact Dates

    Medicare’s Annual Enrollment Period (AEP) runs October 15 to December 7, and anyone with Medicare can join, switch, or drop plans, with changes starting January 1. The Medicare Advantage Open Enrollment Period (OEP) runs January 1 to March 31 and is only for people already in a Medicare Advantage plan. You get one change, effective the first of the month after your plan receives your request.

    TL;DR:

    • Before changing during AEP, review your fall ANOC and EOC, then verify doctors, prescriptions, networks, and total yearly costs for the coming year.
    • OEP permits one change: switch Medicare Advantage plans or return to Original Medicare and add Part D; coverage starts the month after receipt.
    • Leaving Original Medicare for Medicare Advantage generally ends your ability to keep Medigap, and buying it later may require medical underwriting, depending on state rules.
    • Moving outside a plan’s service area, losing creditable coverage, entering or leaving an institution, or qualifying for Extra Help may create a Special Enrollment Period.
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    Table of Contents

    How do AEP and OEP compare side by side?

    Both periods let you adjust coverage, but they are built for different people at different times of year.

    • Dates: AEP runs October 15 to December 7. OEP runs January 1 to March 31.
    • Who can use it: AEP is open to everyone with Medicare. OEP is limited to people already enrolled in a Medicare Advantage plan.
    • AEP actions: join, switch, or drop a Medicare Advantage plan or a Part D drug plan, or move between Original Medicare and Medicare Advantage.
    • OEP actions: switch to a different Medicare Advantage plan, or return to Original Medicare.
    • Limits and timing: AEP changes start January 1. OEP allows one change, effective the first of the month after the plan gets your request, according to Medicare’s enrollment rules.

    What can you do during AEP?

    AEP is an annual window Medicare offers for making coverage changes. Per Medicare.gov, you can join, switch, or drop Medicare Advantage (Part C) and Part D drug plans, or switch between Original Medicare and Medicare Advantage. Whatever you choose takes effect on January 1 of the following year.

    Typical AEP moves include:

    • Moving from Original Medicare into a Medicare Advantage plan
    • Leaving Medicare Advantage to return to Original Medicare and adding a standalone Part D plan
    • Switching to a different Medicare Advantage or Part D plan
    • Dropping a drug plan you no longer need

    You can enroll through Medicare.gov, with the plan directly, or by calling 1-800-MEDICARE. Keep in mind that your request needs to reach the plan by December 7, so don’t wait for the final day.

    Before changing anything, read the Annual Notice of Change (ANOC) and Evidence of Coverage (EOC) your plan sends each fall. Costs, networks, and drug lists often change on January 1 even if you stay put, and Medicare’s own materials note you should review them even if you are satisfied. Check that your doctors remain in network, your prescriptions stay on the formulary, and your total yearly costs still make sense.

    Plan review checks for doctors, prescriptions, and costs

    Pro Tip: Make a list of every medication and doctor you use before you open the ANOC, then check each one against the new plan year line by line.

    Medigap works differently. If you leave Original Medicare for Medicare Advantage, you generally can’t keep a Medigap policy, and buying one later may involve medical underwriting depending on your state. Check with your State Insurance Department or SHIP before dropping a supplement.

    What can you do during OEP, and what can’t you do?

    OEP, formally the Medicare Advantage Open Enrollment Period, runs January 1 to March 31. According to Medicare’s yearly review publication, it is available only to people already in a Medicare Advantage plan. Our guide on Medicare Advantage Open Enrollment goes deeper on the details.

    What you can do:

    • Switch to a different Medicare Advantage plan
    • Drop Medicare Advantage and return to Original Medicare, and join a Part D plan at the same time
    • Make one change only, so choose carefully

    What you cannot do:

    • Join Medicare Advantage from Original Medicare
    • Change or add a drug plan if you stay in Original Medicare without having left Medicare Advantage

    Changes take effect the first day of the month after your plan receives your request. Request a switch on February 10, and your new coverage starts March 1.

    Here are two common scenarios:

    • Your doctor left the network in January. You can move to another Medicare Advantage plan that includes her, but that uses your single OEP change.
    • You never liked the plan’s referral rules. You can return to Original Medicare and add a Part D plan. If you want a Medigap policy afterward, remember it may involve underwriting.

    Pro Tip: Before you submit an OEP request, confirm the new plan covers your doctors and medications, because you won’t get a second try until the next window.

    What if neither period fits your situation?

    Special Enrollment Periods (SEPs) let you change coverage outside AEP and OEP when a qualifying life event happens. According to Medicare.gov, the allowed changes and timing depend on the event. Common triggers include:

    • Moving outside your plan’s service area
    • Losing other creditable coverage
    • Moving into or out of an institution, such as a nursing facility
    • Qualifying for Extra Help with drug costs

    Our overview of SEP events and deadlines covers more triggers. For your exact case, Medicare.gov and your State Health Insurance Assistance Program (SHIP) are the right places to confirm what applies. SHIP counselors offer free, unbiased guidance.

    How do you decide whether to act, and what steps should you take?

    Staying put is a legitimate choice if your plan still works. Consider changing if your provider left the network, your medications moved to a higher cost tier, or your yearly costs jumped. Medicare plans often change benefits, networks, and formularies annually, so last year’s best fit may not be this year’s.

    1. Gather your ANOC and EOC and note what changes on January 1.
    2. Compare your doctors, hospitals, and pharmacies against each plan’s network.
    3. Check every prescription against the formulary and its cost tier.
    4. Add up total yearly costs: premiums, deductibles, copays, and out-of-pocket maximums.
    5. Note the effective date so you know when new coverage begins.
    6. Submit your change through Medicare.gov, directly with the plan, or by calling 1-800-MEDICARE.
    7. Ask your SHIP or a licensed agent to review your choice before the deadline.

    Telehealth access is one detail worth checking when you compare plans. A guide on telehealth coverage can help you weigh virtual-visit benefits. Our enrollment timeline also lays out the key dates in order.

    Pro Tip: Submit your change before the deadline to allow time for processing.

    Where do we stand on helping you through enrollment?

    Most people don’t need more information; they need someone to look at their actual doctors, drugs, and budget. That’s why we start with a holistic health needs assessment, then compare carriers without a thumb on the scale. We review your ANOC, check networks and formularies, work to lower prescription costs, audit your policy every year, and advocate for you on claims. Our Medicare 101 webinar replay is a good place to begin.

    — Core Insurance Solutions

    How can we help you before the next deadline?

    If AEP or OEP is approaching, we can walk through your options with you. Our team offers a Holistic Health Needs Assessment, Unbiased Carrier Comparison, Prescription Cost Optimization, and Annual Policy Audits, all designed to line up your coverage with how you actually use care. Our comparisons are unbiased.

    Core Insurance Solutions

    Start by reviewing our services, or call us to schedule a conversation before your enrollment window closes.

    This article is general information, not a substitute for advice from a qualified financial advisor. Consult a qualified financial professional about your own circumstances before acting on anything here.

    FAQ

    What does OEP stand for in Medicare?

    OEP stands for Open Enrollment Period, and in this context it means the Medicare Advantage Open Enrollment Period. It runs January 1 to March 31 and is only for people already in a Medicare Advantage plan, per Medicare’s yearly review guide.

    What is AEP open enrollment?

    AEP is the Annual Enrollment Period, the yearly window when anyone with Medicare can review and change their health or drug coverage. It runs October 15 to December 7, with changes taking effect January 1, according to Medicare.gov.

    Can you switch from Original Medicare to Medicare Advantage during OEP?

    No. OEP is only for people already in Medicare Advantage, so it can’t be used to join a Medicare Advantage plan from Original Medicare. You would use AEP or a Special Enrollment Period instead.

    Is it better to be on regular Medicare or Medicare Advantage?

    It depends on your doctors, medications, budget, and how much you value predictable costs versus network flexibility. Comparing both against your own health needs each year is the best approach, and our Medigap vs Medicare Advantage guide can help.

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