Yes. You can leave a Medicare Advantage plan and return to Original Medicare during the Annual Enrollment Period, October 15 to December 7, or during the Medicare Advantage Open Enrollment Period, January 1 to March 31. The hard part is not leaving. It is buying the Supplement afterward, because outside a few protected situations a Supplement company can ask about your health and decline you or charge more.
The two windows for leaving
Annual Enrollment, October 15 to December 7: drop Advantage, go back to Original Medicare, and add a standalone drug plan, effective January 1.
Advantage Open Enrollment, January 1 to March 31: if you are already on an Advantage plan, you can switch to another Advantage plan or drop to Original Medicare with a drug plan, one time. Coverage starts the first of the following month.
When you have a guaranteed right to a Supplement
In these cases a Supplement company must sell you a policy with no health questions, as long as you apply within 63 days:
Trial right, first plan: you joined an Advantage plan when you first became eligible at 65 and you leave within the first 12 months.
Trial right, dropped a Supplement: you left a Supplement for your first-ever Advantage plan and you leave within 12 months. You can return to the same Supplement if the company still sells it.
Your plan leaves: the Advantage plan ends, stops serving your area, or you move out of its service area.
The guaranteed-right plans are usually limited to certain letters, such as A, B, D, G, K or L, and Plan G is on that list.
Everyone else: underwriting
After the first year and outside those situations, you apply like anyone else. The company asks about your health history. Conditions such as recent cancer, heart failure, COPD on oxygen, insulin-dependent diabetes with complications or a pending surgery can mean a decline. Some people get approved at a higher rate. Some states have rules that make this easier, so ask me about yours.
This is why the first choice at 65 matters so much. Advantage is easy to enter and can be hard to leave.
If you are inside your first year on Advantage, or your plan is ending, call me now, because the 63-day clock is short. Otherwise request a plan check and I look at whether a Supplement application is likely to be approved before you give anything up.