Medicare open enrollment, explained

Every fall, Medicare's open enrollment period arrives with a wave of advertising that implies everyone must do something before December 7. Most people do not have to, and many of the things the advertisements talk about are not changed in this window at all. The period exists for one purpose: choosing how you get your coverage for the next year, through Original Medicare with a separate drug plan, or through a Medicare Advantage plan.

The dates and what they cover

Open enrollment runs from October 15 to December 7 each year, and a change made in that window takes effect on January 1. Medicare's own page on joining a plan lists what you can do: join a Medicare Advantage plan, switch from one Medicare Advantage plan to another, leave Medicare Advantage and return to Original Medicare, and join, switch or drop a Part D prescription drug plan. The plan has to receive your request by December 7 for the change to start in January.

There is a second, narrower window. From January 1 to March 31, people who are already in a Medicare Advantage plan can switch to a different one or return to Original Medicare with a drug plan. It is a one-time change, and it is not open to anyone who was in Original Medicare on January 1.

What open enrollment is not

It is not the time to sign up for Medicare for the first time; that is the initial enrollment period around your 65th birthday, or a special enrollment period when employer coverage ends. It does not change Part B: the premium and deductible are set by law each year and are the same whichever path you choose. And it does not, on its own, let you move from a Medicare Advantage plan to a Medigap policy with guaranteed acceptance; Medigap has its own rules, and outside the first six months of Part B an insurer can generally underwrite you.

The costs the decision is made against

The 2026 figures on medicare.gov are the baseline for any comparison. The Part B premium is $202.90 a month, more for people whose income two years earlier was above the thresholds, with a $283 annual deductible and then usually 20 percent of the approved amount for each service. Part A is premium-free for most people, with a $1,736 deductible for each hospital benefit period and $217 a day for skilled nursing care from day 21 to day 100. Part D premiums vary by plan.

Those numbers change each January, and the Centers for Medicare & Medicaid Services announces the following year's figures in the fall. The Medicare tracker carries the 2026 amounts and adds the 2027 amounts the day they are published.

Reading the notice your plan sends

If you are in a Medicare Advantage or Part D plan, the plan sends an Annual Notice of Change before open enrollment begins. It is the single most useful document of the season: it lists next year's premium, deductible, copayments and the drugs being added to or removed from the formulary. A plan that was right for you this year can stop being right because one medication moved to a higher tier, and the notice is where that shows.

Two penalties worth knowing about

Medicare charges late-enrollment penalties, and they are permanent. The Part B penalty applies if you did not sign up when first eligible and had no employer coverage to excuse the gap; it is added to the premium for as long as you have Part B. The Part D penalty applies after 63 or more days without drug coverage at least as good as Medicare's, and it too continues for as long as you have Part D. Neither penalty is reset by open enrollment, but the season is a natural moment to close a gap before it grows.

How the January premium reaches you

For most people the Part B premium is deducted from the Social Security payment. That is why the cost-of-living increase that arrives in the same January can look smaller than the announced percentage: the new premium comes out of the new benefit. The Social Security COLA notice, posted to my Social Security accounts in late November, shows both figures.