We need to care for our health. It’s our responsibility to visit our primary care physician regularly. If we put off those appointments, we risk coming down with a medical problem and not even knowing it until later on, when it may have grown more difficult to manage or cure. And if we’re injured or fall suddenly ill, we need to act fast and work with the trained doctors, nurses, and other healthcare professionals who keep us healthy and safe. All of this care, unfortunately, costs money.

Health care isn’t cheap, which is why it’s so important to have health insurance. Medical bills are the number one cause of bankruptcy in the United States, and they’re a lot less manageable when you’re uninsured. America has an employer-based health insurance system, which means that you’ll generally get health insurance as a benefit of employment. But what about when you retire? How will you get health insurance then?

This is what Medicare is for. Since it was started in 1965, Medicare has served as the health insurance solution for older Americans and certain other groups that have difficulty getting healthcare under the employer-based system. When you reach a certain age, you’ll be able to enroll in Medicare. But when do you qualify, and when are you permitted to sign up?

Who qualifies for Medicare?

The simplest and most common way to become qualified for Medicare is to be old enough. Americans qualify for Medicare when they turn 65 years old, provided that they have been paying Medicare taxes for at least 10 years.

Medicare is also available to certain government employees and their spouses. In fact, some, but not all, government jobs offer Medicare as their health insurance plan. Finally, Medicare is available to people with certain disabilities, even if they are under the age of 65.

Medicare is not the same as the government-funded health insurance plan for the economically disadvantaged — that one is Medicaid, and it is a separate program.

When can you sign up for Medicare?

Let’s say you’ve just turned 65 years old, and you are now eligible for Medicare for the first time. Does this mean you can just sign up, even if your birthday is not during the normal open enrollment period for health insurance?

Well, actually, you’ll be automatically enrolled in Medicare when you turn 65 — unless you choose to delay it.

If you postpone your Medicare enrollment, say, because you have a health insurance plan through an employer that you’d rather keep, then you can always switch to Medicare later on.

Generally, you’ll have to make such a switch during the regular enrollment period for Medicare. But there are also things that will trigger a Medicare special enrollment period, allowing you to sign up for Medicare at any time during the year.

What can result in a special enrollment period for Medicare? Generally, anything that could cause you to lose your health insurance or to gain new health insurance options. That includes moving to an area that your current health insurance plan does not cover or that has different health insurance plans available in addition to your current plan. It also includes changing or losing a job and a divorce or the death of a spouse.

Medicare is a great safety net for many Americans, but it can get a bit confusing if you have to worry about special enrollment periods. But don’t worry, there are great guides breaking down Medicare special enrollment periods and great tools for signing up online.