Yes.  If you join a Medicare Advantage plan for the first time, you can leave your Medicare Advantage plan within the first 12 months and join (or return to) a Medicare Supplement [Medigap plan].

In fact, Medicare actually provides two 12-month Medicare Advantage plan "trial periods" allowing you to return to a Medicare Supplement policy with guaranteed issue rights (no medical underwriting) - and, depending on where you live, your state may provide additional guaranteed issue rights for joining a Medicare Supplement.  (For example, California, Connecticut, Massachusetts, Maine, and New York may provide Medicare beneficiaries additional Medigap enrollment rights).

Important:  You will need to use a "trial right" Special Enrollment Period (SEP) to leave your Medicare Advantage plan during the first 12 months so you can join (or re-join) a Medicare Supplement.  You can speak with a Medicare representative to learn more about the SEP (1-800-633-4227).

Trial Right #1 - If you join a Medicare Advantage plan when first eligible for Medicare, you can leave the Medicare Advantage plan within the first 12 months and have a guaranteed issue right to join a Medicare Supplement.

If you joined a Medicare Advantage plan (MA or MAPD) when you were first eligible for Medicare (you turned 65) and within 12 months of joining the Medicare Advantage plan (your trial period), you decide to leave the Medicare Advantage plan, you are provided a Special Enrollment Period to leave your Medicare Advantage plan and a guaranteed issue right to join any Medicare Supplement that is available in your state.

As noted by the Centers for Medicare and Medicaid Services (CMS):

"[If y]ou joined a Medicare Advantage Plan (like an HMO or PPO) or Programs of All-inclusive Care for the Elderly (PACE) when you were first eligible for Medicare Part A at 65, and within the first year of joining, you decide you want to switch to Original Medicare - You have the right to buy [a]ny Medigap policy that's sold in your state by any insurance company."

If you are outside of this 12 month "trial period", you may be subject to medical underwriting, have certain conditions excluded from coverage, or have your Medigap coverage denied (again, some states provide for more generous "guaranteed issue" Medigap rights).


Trial Right #2 - Changing back to your Medigap plan after joining a Medicare Advantage plan

If you were enrolled in a Medicare Supplement and then leave your Medicare Supplement to join a Medicare Advantage plan, you will be granted a Special Enrollment Period to return to your Medigap plan (or other plan if no longer available) within the first 12 months of Medicare Advantage plan enrollment.

Also CMS allows for a "trial period" if:

"[y]ou dropped a Medigap [or Medicare Supplement] policy to join a Medicare Advantage Plan (or to switch to a Medicare SELECT policy) for the first time, you’ve been in the plan less than a year, and you want to switch back - you have the right to buy [t]he Medigap policy you had before you joined the Medicare Advantage Plan or Medicare SELECT policy, if the same insurance company you had before still sells it."

If your former Medicare Supplement is no longer in existence, you will be permitted to join Medicare Supplement Plan A, B, C, F, K, or L. (Remember that Medigap Plan C and Plan F will no longer be accepting enrollments starting in 2020.)

[Source: Choosing a Medigap Policy: A Guide to Health Insurance for People with Medicare, Centers for Medicare and Medicaid Services]

More about the Special Enrollment Period (SEP) for people who dropped their Medigap plan and enrolled in a Medicare Advantage plan for the first time (Trial Right #2).

In Chapter 2 of the Medicare Managed Care Manual "Medicare Advantage Enrollment and disenrollment, the Centers for Medicare and Medicaid Services (CMS) provides a Special Enrollment Period (SEP) for people who left their Medicare Supplement (Medigap plan), joined a Medicare Advantage plan, and now within the trial period wish to return to their Medicare Supplement:

"For Medicare beneficiaries who terminated a Medigap policy when they enrolled for the first time in an MA plan, §1882(s)(3)(B)(v) of the Act provides a guaranteed right to purchase another Medigap policy if they disenroll from the MA plan while they are still in a “trial period.” In most cases, a trial period lasts for 12 months after a person enrolls in an MA plan for the first time.

This SEP is for individuals who are eligible for “guaranteed issue” of a Medigap policy under §1882(s)(3)(B)(v) of the Act upon disenrollment from the MA plan in which they are enrolled. This SEP allows a qualified individual to make a one-time election to disenroll from their first MA plan to join Original Medicare at any time of the year. The SEP begins upon enrollment in the MA plan and ends after 12 months of enrollment or when the beneficiary disenrolls from the MA plan, whichever is earlier."

(Medicare Managed Care Manual, Chapter 2 - Medicare Advantage Enrollment and Disenrollment, Section 30.4.4- SEPs for Exceptional Conditions, 6. SEP for Individuals Who Dropped a Medigap Policy When They Enrolled For the First Time in an MA Plan, and Who Are Still in a “Trial Period”, 42 CFR 422.62(b)(4) (Rev. 1, Issued: July 31, 2018; Effective/Implementation: 01-01-2019) (Updated: August 19, 2011 (Revised: November 16, 2011, August 7, 2012, August 30, 2013, August 14, 2014, July 6, 2015, September 1, 2015, September 14, 2015, December 30, 2015, May 27, 2016, August 25, 2016, June 15, 2017, July 31, 2018 & August 12, 2020)))

Corresponding SEP to join a Medicare Part D PDP when leaving a Medicare Advantage MAPD during Trial Right #2.
Medicare also provides a corresponding Medicare Part D Special Enrollment Period (SEP) for people leaving a Medicare Advantage plan that includes drug coverage (MAPD) during the 12-month “trial” period to also join a stand-alone Medicare Part D prescription drug plan as the re-join their previous Medicare Supplement.

See more in our Frequently Asked Question: "Is there a Special Enrollment to leave a Medicare Advantage plan within the first 12 months and return to my old Medicare Supplement?" 

Question:  Just disenrolling from your Medicare Advantage plan and returning to Original Medicare Part A and Part B?

Aside from the "trial right" Special Enrollment mentioned above, you have several other options if you wish to simply leave your Medicare Advantage plan and return to your Original Medicare Part A and Part B coverage.

During the annual Open Enrollment Period (AEP) or the Medicare Advantage Open Enrollment Period (MA-OEP), you can change Medicare Advantage plans or leave your Medicare Advantage plan and return to original Medicare Part A and Part B.

If your Medicare Advantage plan includes prescription drug coverage (MAPD) or you are leaving an MA-only plan (without drug coverage), you can return to original Medicare Part A and Part B and still enroll in a stand-alone Medicare Part D prescription drug plan (PDP).