Medicare Advantage Open Enrollment Period (MA OEP): Dates, Rules, and What You Can Change

What the MA OEP is and when it happens

The Medicare Advantage Open Enrollment Period, often shortened to MA OEP, is a yearly window that runs from January 1 to March 31. It exists to give people who already have a Medicare Advantage plan a second chance to fine-tune their coverage after the fall enrollment season has ended.

Think of it as a do-over, not a sign-up period. If you joined a Medicare Advantage plan during the fall and discovered in January that your doctor is out of network or your drug is not covered, the MA OEP lets you correct course without waiting until next fall.

• Runs January 1 to March 31, every year.
• Only for people enrolled in a Medicare Advantage plan as of January 1.
• Lets you make one change during the window.

Who can use the MA OEP

Eligibility is the single most misunderstood part of this period. You can only use the MA OEP if you are already enrolled in a Medicare Advantage (Part C) plan as of January 1.

If you have Original Medicare only, you cannot use the MA OEP at all, even to join a Medicare Advantage plan for the first time. To move from Original Medicare into a Medicare Advantage plan, you would need to wait for the fall Annual Enrollment Period (October 15 to December 7) or qualify for a Special Enrollment Period.

• You qualify if you are in a Medicare Advantage plan on January 1.
• You do not qualify if you have Original Medicare only.
• Medicare Advantage MSA (Medical Savings Account) plans are excluded from the MA OEP; those enrollees cannot use this period to make changes.

What you can and cannot do

During the MA OEP you are allowed exactly one change. Once you make that change, the window is effectively closed for you until next year, so it pays to be sure before you act.

• You CAN switch to a different Medicare Advantage plan, with or without prescription drug coverage.
• You CAN drop your Medicare Advantage plan and return to Original Medicare.
• If you return to Original Medicare, you CAN also join a standalone Part D drug plan during the same window.
• You CANNOT switch from Original Medicare into a Medicare Advantage plan during the MA OEP.
• You CANNOT switch from one standalone Part D drug plan to another, or newly join a Part D plan, while staying on Original Medicare. Those changes belong to the fall Open Enrollment Period.
• You CANNOT make a second change after using your one allowed change.

When coverage starts and how the MA OEP differs from the fall AEP

When you make a change during the MA OEP, your new coverage starts on the first day of the month after the plan receives your enrollment request. For example, a change submitted in February generally takes effect March 1.

It is easy to confuse the MA OEP with the fall Annual Enrollment Period (AEP). They are two different periods with different rules.

• MA OEP: January 1 to March 31. Only current Medicare Advantage enrollees. One change allowed. New coverage starts the first of the following month.
• Fall AEP: October 15 to December 7. Open to everyone with Medicare. Unlimited changes (the last one on file counts). Changes take effect January 1.
• If you miss the AEP, the MA OEP is a limited backup, but only if you already had a Medicare Advantage plan.

Medigap rights and costs if you return to Original Medicare

Leaving a Medicare Advantage plan during the MA OEP can affect your Medigap (Medicare Supplement) options, and this is where many people get surprised. Switching from one Medicare Advantage plan to another does not create any Medigap guaranteed-issue right.

If you return to Original Medicare, you generally have 63 days after your Medicare Advantage coverage ends to buy a Medigap policy, but a guaranteed-issue right (meaning an insurer cannot turn you down or charge more for health reasons) applies only in limited situations. One important example is the Medigap trial right: if you joined a Medicare Advantage plan when you first became eligible for Medicare at 65 (or dropped a Medigap policy to do so), you have a single 12-month trial period to return to Original Medicare with special guaranteed rights to buy a Medigap policy. Outside of these specific situations, an insurer may use medical underwriting, so it is wise to confirm you can get a Medigap policy before you drop your Medicare Advantage plan.

Returning to Original Medicare also brings its own 2026 costs. The standard Part B premium is $202.90 per month with a $283 annual deductible, after which Original Medicare generally pays 80% and you pay 20% of covered Part B services. If you go back to Original Medicare and want drug coverage, joining a standalone Part D plan matters: the 2026 national base beneficiary premium is $38.99 per month, the annual out-of-pocket cap on covered drugs is $2,100, and there is a late enrollment penalty if you go without creditable drug coverage.

• Switching Medicare Advantage plans: no Medigap guaranteed-issue right.
• Returning to Original Medicare: generally 63 days to buy Medigap, but guaranteed-issue only in limited cases such as the trial right.
• 2026 Part B: $202.90/month premium, $283 annual deductible, then you pay 20% of covered services.
• 2026 Part D: $38.99/month national base premium, $2,100 annual out-of-pocket cap on covered drugs.
• Part D late enrollment penalty: 1% of $38.99 multiplied by the number of full months you went without creditable drug coverage, rounded to the nearest $0.10, added for as long as you have Part D.

How to make a change during the MA OEP

Making a change is straightforward, and you have several ways to do it. Whichever method you choose, keep a record of the date you submitted your request, since coverage timing depends on when the plan receives it.

• Enroll online at Medicare.gov.
• Contact the plan you want to join directly.
• Call 1-800-MEDICARE (1-800-633-4227), available 24 hours a day, 7 days a week.