Whether you’re new to Medicare or looking to improve your coverage, you need to pay attention to some important Medicare enrollment dates. Otherwise, you could face stiff penalties or miss out on valuable benefits, possibly forever.

The deadlines for signing up or changing plans differ, depending on whether you’re new to the program or are already receiving benefits. 

The consequences of not understanding these key dates: You could end up paying far more for Medicare—for the rest of your life—going months without insurance, or even being denied coverage due to a pre-existing condition.

Here’s what you need to know to get the best coverage at the most affordable price.

If you’re new to Medicare

For the most part, you qualify for Medicare based on your age—or, occasionally, due to a disability. Your first enrollment period is crucial, as missing this window will almost certainly result in higher premiums.

Your 65th birthday: Happy birthday! As a birthday present, Uncle Sam gives you Medicare.

Your Initial Enrollment Period (IEP) spans the three months prior to your 65th birthday, your birthday month, and three months afterwards.

If you’re already receiving Social Security, you’ll be automatically enrolled in Original Medicare, or Parts A & B, at this time. But enrolling in a private Medicare Advantage plan (Part C) or a Medicare Prescription Drug Plan (Part D) is up to you. If you’re not yet getting Social Security, you’ll need to apply for Parts A through D on your own.

While you can enroll any time during this seven-month window, the date you sign up affects when your coverage begins (see below). And if you wait until after your birthday, you may face a delay.

The date you retire, or lose employer benefits: In general, if you’re still getting health insurance from your or your spouse’s employer at age 65, you don’t need to drop it to enroll in Medicare (though you can). Instead, you’ll qualify for a Special Enrollment Period (SEP) that starts when that coverage ends.

For Original Medicare, this SEP lasts eight months, but for the private Medicare Advantage (Part C) and Prescription Drug Plan (Part D) coverage, you have only 63 days after your employer insurance ends.

One caveat: If you work for a very small company (fewer than 20 employees), Medicare may not recognize your work health plan as “credible coverage,” and you’ll risk penalties by not signing up at age 65 (more on those below). Check with your employer to make sure.

When you’re signed up for Part B: Once you’re 65 and enrolled in Part B, you’re eligible for to buy a Medigap, or a Medicare Supplement, policy. Your six-month Medigap open enrollment period starts the first day of the month after you turn 65 and are enrolled in Part B. During that time, you can purchase Medigap without being subject to medical underwriting.

If you’re already enrolled in Medicare…or should be

Once you’ve already signed up for Medicare, you don’t need to re-elect coverage every year: You remain enrolled in the last plan you signed up for.

That said, plan coverage and costs can change—and your health can change, too. So it’s worth going through the exercise of comparing plans annually to ensure that yours still fits your needs.

October 15 to December 7: These 53 days are known as the Annual Election Period (AEP), or Medicare open enrollment, and it’s when you can change your Medicare Advantage plan (Part C) or Prescription Drug Plan (Part D).

Plans you sign up for during the AEP become effective on January 1 of the following year.

January 1 to March 31: The first three months of the year are known as the General Election Period.

If you missed signing up for Medicare when you first became eligible, you can enroll in Original Medicare at this time. Your coverage won’t start until July 1, however, and you might have to pay a higher premium—forever.

Beginning on January 1 to March 31 each year is also the Medicare Advantage Open Enrollment Period, when anyone with an Advantage plan can drop it and enroll in a different one.

Alternatively, you can use this window to bail out of Medicare Advantage and sign up for Original Medicare, plus Part D.

What missing out will cost you

Say you’re 65 and in good health, and you don’t want to pay Medicare premiums. So why sign up? Because the government imposes stiff penalties if you don’t.

Original Medicare. For Part B, your premium will be 10% higher for each 12-month period in which you were eligible but didn’t sign up.

So if you delay signing up for Part B for 28 months after your IEP ends, your premiums will be 20% higher than they would have been if you’d signed up as soon as you were eligible. And that penalty stays in effect for as long as you remain on Medicare.

Medicare Part D. With a prescription drug plan, a late enrollment penalty may apply if your IEP ends and you don’t have Part D or any other creditable drug coverage for 63 or more days in a row.

The penalty for Part D has a complicated calculation. You’ll pay an extra 1% of the “national base beneficiary premium,” or an estimated average of current Part D monthly plan costs, multiplied by the number of months you delayed enrollment. For 2024, the national base beneficiary premium is $34.70.

You’ll pay this penalty for as long as you’re enrolled in Part D, and it could go up, since the national base beneficiary premium changes each year.

So even if you don’t think you need a Prescription Drug Plan, you may want to enroll anyway to avoid paying higher premiums if you want coverage later.

Medigap. You won’t necessarily be subject to a higher premium if you don’t sign up for a Medicare Supplement policy when you first become eligible. But your premium could be higher, based on your health and pre-existing conditions. You could also have certain pre-existing conditions excluded for a certain period of time, or even be outright denied coverage.

Medicare is as simple as you make it

If you prefer to be in control, make informed decisions and don’t waste time, this is for you.

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Article updated on October 27, 2023