There are two primary ways to get Medicare coverage — Original Medicare (Part A and Part B) or a Medicare Advantage plan (Part C). You may also need other coverage, including Medicare prescription Part D or supplement insurance.

In 2019, 64 million people nationwide were enrolled in some form of Medicare. A majority received Original Medicare, but about 34 percent — or 23 million — were enrolled in Medicare Advantage plans. Original Medicare is administered by the U.S. Centers for Medicare & Medicaid Services, while Medicare Advantage is fulfilled through private insurance companies that have been pre-approved by the federal government.

Most Americans become eligible for Medicare as they approach retirement and their 65th birthday. Information from the U.S. Centers for Medicare & Medicaid Services begins arriving in the mail, and decisions need to be made within a certain time frame to avoid costly penalties.

If you are already receiving Social Security benefits when you turn 65, the government automatically enrolls you in both Medicare Part A and Part B. So, if you’re already claiming Social Security, enrollment might be as simple as opening your mail and placing your new Medicare card in your wallet. Your Medicare card should arrive three months prior to your 65th birthday.

Your Medicare coverage will begin on the first day of the month you were born. For example, if your birthday is August 12, your coverage begins Aug. 1.

If you aren’t collecting Social Security at age 65, you have a seven-month window to enroll in Medicare. This window opens three months before you turn 65 and closes three months after the last day of your birth month. It’s important to act quickly, or you could face delays and penalties, according to Medicare.gov.

Some people choose not to enroll in Part B coverage from Medicare when they turn 65 because they still receive insurance through their current employer or their spouse’s current employer. You can choose to remain on your current insurance for as long as you or your spouse receives employer sponsored benefits. When you eventually retire, you will have an eight-month enrollment period during which you may sign up for Part B without incurring a late penalty.

If you’re covered by your employer’s group health plan but will be aging into Medicare soon, speak with your Human Resources department about your transition to avoid mistakes and unnecessary costs.

People are also automatically enrolled in Medicare after receiving disability benefits for two years. Patients with end stage renal disease or amyotrophic lateral sclerosis (also known as ALS and Lou Gehrig’s disease) are eligible for Medicare without having collected disability for 24 months.