Here's what you need to know if you want to change Medicare Advantage Plan

Yes, Medicare’s annual enrollment period ended Dec. 7.

No, not all hope is lost if you realize the Advantage Plan you picked for 2021 is a mismatch.

That’s because Medicare has a three-month window at the beginning of each year, Jan. 1 through March 31, when you can swap your Advantage Plan for another or drop it and return to basic Medicare (Part A hospital coverage and Part B outpatient coverage).

More from Personal Finance:
Trump’s plan for $200 Medicare drug cards advances
Not all end-of-life decisions are covered in a will
Avoid mistakes when divvying up assets in divorce

“The most common reason people change is that they joined a plan during the [fall enrollment window] without realizing that one of their doctors is not in the network or one of their medications is not covered on the formulary,” said Danielle Roberts, co-founder of insurance firm Boomer Benefits.

Also from Jan. 1 through March 31: If you missed your initial Medicare enrollment period and don’t qualify for an exception, you can sign up during that time. If this is your situation, coverage won’t start until July 1, said Elizabeth Gavino, founder of Lewin & Gavino and an independent broker and general agent for Medicare plans.

Of Medicare’s 63 million or so beneficiaries, about 25 million are enrolled in an Advantage Plan, which delivers Parts A and B and usually Part D prescription drug coverage, along with extras such as dental and vision.

The upcoming three-month opportunity to change or drop your Advantage Plan will arrive just weeks after the close of Medicare’s annual fall enrollment, when a variety of options were available for those who wanted to modify their coverage.

In contrast, the upcoming Advantage Plan-related window comes with restrictions.

For starters, you can only make one switch. This means that once you move to a different Advantage Plan or drop it for basic Medicare, the change is generally locked in for 2021 (unless you meet an exclusion that qualifies you for a special enrollment period).

Additionally, this three-month window does not allow you to switch from one stand-alone Part D prescription drug plan to another.

If you picked a Part D plan in the fall open enrollment period based on faulty or misleading information, you can call 1-800-Medicare at any point during the year to see if your situation would allow you to make a change.

Meanwhile, dropping an Advantage Plan in favor of basic Medicare often means losing drug coverage — which means you would have to enroll in a stand-alone Part D plan. This matters, because if you go 63 days without the coverage, you could face a lifelong late-enrollment penalty that gets tacked on to your monthly premiums.

Also, if you switch back to original Medicare and want to get a supplemental policy (aka “Medigap”), be aware that you may not qualify for guaranteed coverage. These policies either fully or partially cover cost-sharing of some aspects of parts A and B, including deductibles, copays and coinsurance. However, they come their own rules for enrolling.

“If someone plans to … go back to original Medicare and get a Medigap plan, they should be aware that they will likely have to answer health questions and go through underwriting,” Roberts said.

She advises starting the process by applying for the Medigap plan and getting approval before leaving the Advantage Plan or enrolling in a standalone Part D plan. 

“Enrolling in the Part D plan will boot them out of the Medicare Advantage plan, so it’s important to wait on that part as well,” Roberts said. “We encourage people who need to make a change to do it early in the election period.”