Medicare Open Enrollment Period: Dates, Rules, and What You Can Change

Medicare has multiple enrollment periods with different names, different dates, and different rules about what you're allowed to change. Confusing them is easy — and the wrong assumption can lock you out of coverage changes for an entire year.

Here are the three main windows and exactly what each one lets you do.

Annual Enrollment Period (October 15 – December 7)

This is the big one. Also called the "Fall Open Enrollment Period," it runs every year from October 15 through December 7. Changes take effect January 1.

What you can do:

• Switch from Original Medicare to Medicare Advantage (or vice versa)
• Change from one Medicare Advantage plan to another
• Join, switch, or drop a standalone Part D prescription drug plan
• Drop Medicare Advantage and return to Original Medicare (and add a Part D plan)

What you cannot do:

• Enroll in Part A or Part B for the first time (that's the Initial Enrollment Period)
• Buy or change Medigap plans (those have their own enrollment rules)
• Change your Part B coverage level

This is your annual chance to review whether your current plan still makes sense — especially if your medications, doctors, or financial situation changed.

Medicare Advantage Open Enrollment Period (January 1 – March 31)

This is a narrower window, available only to people already enrolled in a Medicare Advantage plan.

What you can do:

• Switch from one Medicare Advantage plan to a different one
• Drop Medicare Advantage and return to Original Medicare, and enroll in a standalone Part D plan

What you cannot do:

• Switch from Original Medicare to Medicare Advantage (that's the Annual Enrollment Period)
• Make any Part A or Part B changes

If you picked a Medicare Advantage plan during the fall and realized the network doesn't include your preferred doctors, this January–March window is your safety valve.

General Enrollment Period (January 1 – March 31)

Different name, different purpose. The General Enrollment Period is for people who missed their Initial Enrollment Period and need to sign up for Part A or Part B for the first time.

What you can do:

• Enroll in Part A
• Enroll in Part B

Coverage start: The first day of the month after SSA receives your completed application.

The catch: Late enrollment penalties apply. If you could have had Part B but didn't (and didn't have qualifying employer coverage), you'll pay a 10% premium surcharge for each full 12-month period of delay. This surcharge is permanent.

Which Period Do You Need?

One Period You Can't Afford to Miss

The most consequential window is the one most people don't think of as an "enrollment period" — the Medigap Open Enrollment Period. It's a one-time, 6-month window starting the first month your Part B is active at age 65 or older. During these six months, you can buy any Medigap plan without medical underwriting. After it closes, most states allow insurers to deny coverage or charge higher premiums based on your health.

The Medicare Enrollment Guide covers every enrollment window — initial, special, annual, and general — with specific timelines and the exact steps for each scenario.

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