Joining Medicare Advantage is easy. Leaving is not.

Every autumn the choice arrives as a pair of doors. Behind one is Original Medicare, run by the federal government, with a private Medicare Supplement Insurance policy, usually called Medigap, sold alongside it to cover the share Medicare leaves behind. Behind the other is Medicare Advantage, a private plan paid by the government to deliver the same benefits, usually with drug coverage folded in and a list of extras attached.

Both doors are open. Anyone with Part A and Part B who lives in a plan's service area can join a Medicare Advantage plan, in any year, with any pre-existing condition. Anyone already in a Medicare Advantage plan can return to Original Medicare in the right window.

Coming back, the doors are not the same width. Returning to Original Medicare is straightforward. Returning to Original Medicare and buying the Medigap policy that caps what Original Medicare leaves open is a separate question with a separate answer, because for most people the right to buy that policy lasted six months and then expired.

How the country has split

Neither door is the unusual choice. In calendar year 2025, average monthly enrollment ran 34.9 million people in Medicare Advantage against 34.0 million in Original Medicare. The remainder of the 69.4 million people holding Part A, Part B or both sat in other kinds of health plan. The country is split close to evenly, and the split has been moving toward Advantage for years.

What this guide covers

What each door costs in 2026, in the actual published amounts. What the Advantage plan's yearly spending limit counts and, more usefully, what it does not. The six month window that decides whether a Medigap policy can be bought at all. The two trial rights that are the only clean way back once that window has closed. And the two enrollment periods each year, with the exact list of what each one is allowed to change.

This guide is educational information. It is not legal, tax or financial advice.

Original Medicare is two parts with two different billing habits. Part A covers inpatient hospital care, skilled nursing facility care, hospice and some home health care, and it charges by the stay. Part B covers doctors, outpatient care, tests, equipment and most preventive services, and it charges by the year and then by the visit.

Part A charges by the benefit period, not by the year

Part A costs no premium at all for anyone who paid Medicare taxes long enough to qualify, which is most people reaching 65. Anyone who did not buys in: $311 a month with at least 30 quarters of coverage, or married to someone who has them, and $565 a month with fewer.

What Part A charges instead is a deductible of $1,736 in 2026, and that deductible is per benefit period rather than per year. A benefit period ends after 60 days in a row with no inpatient or skilled nursing care. Medicare's own handbook is blunt about the consequence: a new benefit period means paying the deductible again, and that can happen more than once in a single calendar year.

Part B charges a premium, a deductible and then a percentage

The standard Part B premium in 2026 is $202.90 a month, up $17.90 from $185.00 in 2025. Higher incomes pay more, on a scale read from a tax return filed two years earlier, rising to $689.90 a month at $500,000 or more filing alone and $750,000 or more filing jointly.

After the premium comes an annual deductible of $283. After the deductible, Part B pays its share and the patient pays 20 percent of the Medicare-approved amount for most services.

The sentence the whole choice turns on

That 20 percent has no ceiling. The Medicare handbook states it in one line: there is no yearly limit on what a person pays out of pocket under Original Medicare unless they hold supplemental coverage such as Medigap, Medicaid, or employer, retiree or union coverage.

Twenty percent of an ordinary year is a small number. Twenty percent of a cardiac surgery, a course of chemotherapy or a long run of outpatient infusions is not, and nothing inside the program stops it climbing. Original Medicare on its own is excellent coverage with an open-ended tail.