The Medicare Annual Enrollment Period (AEP) lasts from October 15 through December 7. But every year, despite the seemingly endless reminders seen on TV and in your mailbox, millions of Medicare beneficiaries miss the Annual Enrollment deadline. In fact, more than 4 in 10 (43%) people on Medicare didn't even review their current coverage during the annual enrollment period to see if there were changes to their premiums and out-of-pocket expenses, according to KFF.org. If this describes you, don't panic! If you did want to make changes to your Medicare coverage, you may have options.

Do you qualify for the Medicare Annual Enrollment Period?

First things first: Are you a current Medicare beneficiary? The Medicare Annual Enrollment Period is only for current Medicare beneficiaries. If you are in your Initial Enrollment Period (IEP), then you are not limited to the AEP window. You have 7 full months to choose your Medicare coverage.

Your Medicare Initial Enrollment Period begins 3 months before the month you become eligible for Medicare and ends 3 months after your eligibility month. This is true whether you age into the program or qualify for Medicare due to illness or disability.

For example, if your birthday or 25th month of collecting Social Security disability benefits occurs in May, then your IEP begins February 1 and ends on August 31. However, if your birthday falls on the 1st of the month, your IEP begins and ends one month earlier. In this example, a birthday of May 1 gives you an IEP window that opens on January 1 and closes July 31.

If you began receiving Railroad Retirement Board (RRB) or Social Security benefits at least 4 months before turning 65, Medicare enrollment is automatic. Everyone else must choose to sign up for Medicare. You do so through the Social Security website by clicking here.

Did you miss your Initial Enrollment Period?

If you missed your Initial Enrollment Period AND you don't qualify for a Special Enrollment Period (SEP, more on this in a moment), you cannot sign up for Medicare during AEP. Again, this is the time for current Medicare beneficiaries to make changes to their Medicare coverage.

In this instance, you need to wait for the Medicare General Enrollment Period, which occurs every year from January 1 through March 31. During this 3-month window, you may sign up for Medicare Part A, hospital insurance, and Medicare Part B, medical insurance.

Once the General Enrollment Period ends, you have from April 1 through June 30 to sign up for a Medicare Part C (more commonly known as Medicare Advantage) and/or a Medicare Part D prescription drug plan. Whether you choose Original Medicare or an Advantage plan, your coverage begins the month after you make your selections.

Depending on how long you went without creditable coverage (i.e. health insurance that is comparable to Medicare in terms of both cost and benefits), you may owe late enrollment penalties. We describe the Medicare Part B late enrollment penalty here and the Part D penalty is explained here. Very few people owe a late penalty for Medicare Part A simply because very few people pay the Part A premium (around 1%).

Do you have a Medicare Advantage plan?

If you are currently enrolled in a Medicare Advantage (MA) plan, you may make changes to your coverage during the Medicare Advantage Open Enrollment Period (OEP).  This occurs every year from January 1 through March 31. Your options during OEP include:

• Switching from one Advantage plan to another
• Leaving your Part C plan to return to Original Medicare (Parts A and B)

If making either change results in you losing your prescription drug coverage, you may also enroll in a Medicare Part D prescription drug plan during OEP.

You can't do everything during Medicare Advantage Open Enrollment that you can during AEP, however.  Changes you cannot make during OEP include:

• Leaving Original Medicare to join a Medicare Advantage plan
• Signing up for a standalone Part D plan if you did not lose prescription drug coverage due to changing your MA plan
• Changing from one standalone Part D plan to another

You are limited to one change during the Medicare Advantage Open Enrollment Period. Your changes will take effect the month after the plan receives your request.

Are you eligible for a Medicare Special Enrollment Period?

If you qualify for a Special Enrollment Period, you may sign up for Medicare or make changes to your coverage outside of the Annual Enrollment Period.

One of the most common reasons people qualify for an SEP is because they had creditable coverage through an employer (theirs or their spouse's) at the time they became eligible for Medicare. There are literally dozens of ways to qualify for an SEP, but they fall under four main categories:

• Change of address
• Loss of current coverage
• Having a chance to get other coverage
• Your plan's contract with Medicare changed

There is also a miscellaneous type category that includes life changes like becoming eligible for Medicaid and qualifying for Extra Help. Find the full list of special circumstances, including guidelines for how long you have to act, on Medicare.gov.

Compare your Medicare plan options

Our Find a Plan tool makes it easy to compare the costs and benefits of Medicare plans in your area. Simply enter your zip code to review Advantage, Part D, and Medicare Supplement Insurance plans.

Additional resources

• ClearMatch Medicare: Find a Medicare Plan
• Social Security Administration: Medicare Benefits