When to Sign Up for Medicare: Key Enrollment Periods Explained 

October 19, 2026 | Tags: Medicare

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Once you know the A, B, Cs and Ds of Medicare and understand the differences between Medicare Advantage and Medicare Supplement, the next step is knowing when to sign up. Medicare has several enrollment periods. The right enrollment period depends on whether you are signing up for the first time, changing plans or enrolling after employer coverage ends. Here are the key Medicare enrollment periods and when each one applies.

When is the Medicare Initial Enrollment Period?

If you are approaching age 65, you can enroll in Medicare for the first time during your Initial Enrollment Period, or IEP. This seven-month period includes:

• The three months before the month of your 65th birthday.
• The month you turn 65.
• The three months after your 65th birthday.

If you are still working and have coverage through your employer’s or spouse’s group health plan when you turn 65, you may be able to delay Medicare enrollment. In this case:

• You may be able to enroll when you retire.
• You have eight months to enroll in Medicare after your employment or group health coverage ends, whichever occurs first.
• The size of the employer can affect whether you can delay enrolling in Medicare Part A and Part B without paying a penalty. If your employer or your spouse’s employer has 20 or more employees, talk with the employer for more information about delaying enrollment.

You must enroll in Original Medicare (Part A and Part B) before you can enroll in a Medicare Advantage (Part C) or Medicare Supplement plan.

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When is the Medicare General Enrollment Period?

If you miss your IEP window, you can enroll in Original Medicare during the next General Enrollment Period (GEP). You may have to pay a higher premium for enrolling late in Medicare Part A or Part B. Here are the key dates:

• Jan. 1 through March 31: Enroll in Original Medicare.
• April 1 through June 30: Enroll in a Medicare Advantage or Medicare Part D prescription drug plan.
• July 1 of the same year: Coverage begins.

When is the Medicare Annual Enrollment Period?

The Medicare Annual Enrollment Period, or AEP, runs from Oct. 15 through Dec. 7 each year. During AEP, you can enroll in a Medicare Advantage plan or change your existing Medicare Advantage plan or prescription drug plan. Changes made during AEP take effect on January 1 of the following year.

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When is the Medicare Supplement Open Enrollment Period?

The best time to enroll in a Medicare Supplement plan is during your six-month Medicare Supplement Open Enrollment Period. This period begins three months before your 65th birthday and ends three months after it. You must also be enrolled in Medicare Part B. You may apply for Medicare Supplement coverage outside this six-month period. However, you may pay a higher premium or be denied coverage based on your medical history.

You cannot enroll in a Medicare Advantage plan and a Medicare Supplement Plan at the same time.

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What is a Medicare Special Enrollment Period?

Certain situations may allow you to change your Medicare Advantage plan outside of AEP. This opportunity is called a Special Enrollment Period, or SEP. Each SEP has its own rules. You may qualify after:

• Moving into or outside your plan’s service area.
• Qualifying for Extra Help, also called the Low-Income Subsidy.
• Moving into a nursing home or another institution.
• Becoming eligible for both Medicare and Medicaid.
• Losing employer coverage.

If you have questions about whether you qualify for an SEP or any of the other enrollment periods, you can speak to a licensed Medical Mutual agent by calling toll free at 1-866-406-8777 (TTY: 711). For more details on enrollment periods, visit Medicare.gov or download our Understanding Medicare Guide.