The cost of healthcare can be astronomical at any age. And unfortunately, many retirees find that their healthcare needs increase at a time when they give up their jobs and the health insurance that goes with them.

Thankfully, seniors can fall back on Medicare to cover their health-related needs. If you're gearing up to enroll in Medicare, here are some essential things to know.

Two smiling people at a laptop.

Image source: Getty Images.

1. You can sign up before your 65th birthday

Medicare eligibility begins at age 65, but you can sign up a bit sooner.

Your initial enrollment window begins three months before the month of your 65th birthday and ends three months after that month. All told, you get seven months to sign up. But if you want to have coverage in place by the time you turn 65, it pays to get the ball rolling sooner.

There can be penalties for not signing up for Medicare during your initial enrollment period. If you're covered by a qualified group health plan at age 65 and delay your enrollment, these shouldn't apply. But otherwise, waiting to enroll in Medicare could result in a 10% surcharge on your Part B premiums for each 12-month period you were eligible for coverage but didn't sign up.

2. You can sign up even if you're not on Social Security

You can start claiming Social Security once you turn 62, so it's conceivable you might already be collecting benefits once you become eligible for Medicare. In this situation, you'll actually be enrolled in Medicare automatically come age 65.

But you don't need to be collecting Social Security to sign up for Medicare. So if you're waiting longer to file for benefits, it still pays to enroll in Medicare at 65 if you need the health coverage and/or want to avoid lifelong penalties.

3. Medicare Advantage may be a better choice for you

Coverage under original Medicare consists of Part A, which covers hospital care, Part B, which covers outpatient services, and Part D, which covers prescription drugs. But you may decide to enroll in Medicare Advantage, instead. Doing so could work to your benefit.

Medicare Advantage plans are offered by private insurers and limit you to a more narrow network of providers than original Medicare. But some Advantage plans offer more comprehensive coverage than original Medicare -- and at a lower cost.

For example, most Medicare Advantage plans will cover dental cleaning and eye exams, whereas original Medicare won't pick up the tab for these services. So it pays to explore your options under Medicare Advantage before assuming that original Medicare is your best choice.

There's lots to know about Medicare enrollment and coverage. Your best bet, therefore, is to read up on the program well ahead of your 65th birthday so you know what to expect. The more you educate yourself on Medicare, the better equipped you'll be to sign up at the right time and choose the plan that's best for you.