The main Medicare open enrollment period runs from Oct. 15 through Dec. 7.

During this period, anyone enrolled in original Medicare, Medicare Advantage, or a Part D drug plan can adjust their coverage. Because Medicare offers two main paths — original Medicare (Parts A and B) or Medicare Advantage (Part C) — you should shop around during open enrollment to find the option that best fits your needs and lifestyle.

Medicare beneficiaries who already have Part A and Part B can use this election period to enroll in, change, or disenroll from a Part D plan or join a Medicare Advantage plan. Medicare Advantage plan participants can switch Advantage plans or return to original Medicare.

When is the open enrollment period?

Medicare open enrollment, also known as the annual election period (AEP), runs from October 15 to December 7 each year. During this period, you can switch from original Medicare to a Medicare Advantage plan, or vice versa. You can also choose a new Advantage or new Medicare Part D prescription drug plan. Coverage will begin in 2027.

If you decide you want to keep your current plan(s), you don’t have to do anything. Your current selections will be automatically renewed.

When is the Medicare Advantage Open Enrollment Period (MAOEP)?

Medicare Advantage plan enrollees have a second window of opportunity to change their minds after the primary open enrollment period ends. If you enroll in a Medicare Advantage plan and, for any reason, you don’t like it, you can disenroll during the MAOEP that runs from Jan. 1 through March 31. This only applies to people already enrolled in Medicare Advantage plans who want to make a change.

During this period, you can disenroll from a Medicare Advantage plan and return to original Medicare, with or without a Part D drug plan, or switch from one Medicare Advantage plan to another Medicare Advantage plan. If you decide to switch to original Medicare, consider purchasing a Medigap policy.

When is the General Enrollment Period (GEP)?

The general enrollment period (GEP) that runs from January 1 through March 31 is for eligible beneficiaries who didn’t sign up for Medicare when they turned 65 and don’t qualify for a special enrollment period (or SEP, see description below).

If you missed your initial enrollment period (IEP), this is when you can sign up for Parts A and B. Unfortunately, you will likely have to pay a Part B premium penalty.

If you have to pay for Part A, and you sign up for Part B during the GEP, you can also join a Medicare Part D drug plan. You’ll have two months after signing up for Part B to join a drug plan. Your drug coverage will start the month after the plan receives your request to join.

When you enroll in the GEP, your coverage begins on the first of the month after you enroll. For example, if you enroll in January, your coverage begins Feb. 1.

What is the Special Enrollment Period (SEP)?

After your IEP has past, you might have a chance to sign up for Medicare during a special enrollment period (SEP).

If you experience a qualifying life event, you may be able to enroll or change a selection without having to pay a late enrollment penalty. You might also qualify for a SEP if you miss your open enrollment period after joining Medicare and want to change your selections.

The Medicare site offers a Q&A on how to qualify for the special enrollment period to give you a general explanation of qualifying circumstances.

Qualifying life events for special enrollment:

If you miss an enrollment period because of an exceptional condition, you’ll have two months to join a Medicare Advantage plan (with or without Part D drug coverage) or a Medicare Part D drug plan. Your coverage will start the first day of the month after the Medicare Advantage or Part D Plan receives your request to join.

Waiver of the Part B enrollment penalty. If you don’t sign up for Part B when you’re first eligible, you might have to pay a late enrollment penalty for as long as you have Part B. Your monthly Part B premium might go up 10% for each full 12 months in the period that you could’ve had Part B, but didn’t sign up. If you’re allowed to sign up for Part B during a SEP, you usually don’t pay a late enrollment penalty.

Help choosing a plan

Medicare provides an excellent tool to help you compare the costs of different Medigap, Medicare Advantage and Part D prescription drug plans. The tool will tell you the out-of-pocket maximum and what your specific medications would cost under different Medicare Advantage plans. It can also provide price ranges for Medigap plans available in your area.

You can always call Medicare for assistance at 1-800-MEDICARE (1-800-633-4227). Local State Health Insurance Assistance Programs (SHIPs) provide unbiased, personalized counseling.

(Donna LeValley is a retirement writer for Kiplinger.com.)

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