Medicare provides health coverage for millions of seniors, and if you're gearing up to enroll, it pays to know what to expect. Here are a few key pieces of information to keep in mind.

1. You get a seven-month window to enroll initially

Medicare eligibility begins at age 65, but you can actually sign up a bit ahead of your 65th birthday to get the ball rolling. Your initial enrollment window spans seven months, beginning three months ahead of the month of your 65th birthday and ending three months after that month. If you sign up a month or so after turning 65, you'll be eligible for retroactive benefits dating back to your 65th birthday.

Medicare enrollment form


2. You can sign up online

Many seniors sign up for Medicare by calling Social Security at 1-800-772-1213, or by visiting a local Social Security office. Those methods are a fine way to enroll, but they may prove time-consuming. A better bet, therefore, could be to enroll online. Doing so should take under 30 minutes, and the process is easy.

You'll start by creating an account on the Social Security Administration's website. You'll then need to provide some personal information, like your Social Security number, and answer some other questions to confirm your identity. You'll be asked whether you want to sign up for Medicare alone, or Medicare in conjunction with Social Security, and if you're not ready to start collecting benefits, you can opt for Medicare by itself.

3. It pays to enroll on time

Signing up for Medicare during your initial enrollment window will ensure that you have coverage in place when you need it. But here's another reason to enroll in Medicare on time: If you don't, you'll risk lifelong surcharges on your Part B premiums. Specifically, you'll face a 10% increase for each year-long period you were eligible for Medicare coverage but failed to enroll.

4. You can sign up for Medicare even if you already have health coverage

Many people continue to work once they turn 65, and as such, have health insurance through an employer. If that's the case, you don't have to sign up for Medicare right away, and you'll be given a special enrollment period later on that can help you avoid the surcharges we just talked about (this assumes you have access to a group health plan covering 20 people or more).

However, if you want to retain your employer health coverage and also get coverage through Medicare, you're allowed to do so. In that case, you'd use Medicare as secondary insurance. In fact, what you may want to do is sign up for Part A only, since it's free, and use it for hospital coverage to fill in gaps your employer's insurance plan leaves you financially responsible for. The only caveat is that once you enroll in Medicare, you can no longer contribute to a health savings account, so keep that in mind if you're thinking of signing up when you already have insurance.

There's a lot to know about Medicare, so if you're planning to enroll in the near future, do some reading to see what to expect. The more you educate yourself, the easier it will be to make the most of your benefits.