Many workers rely on their employers to provide them with health coverage. So when the time comes to leave the workforce for good, you'll generally need to secure coverage on your own.

That's where Medicare comes in. You can sign up for Medicare independently of Social Security, and you can make changes to your coverage year after year to align with your healthcare needs.

But there's a lot of misinformation out there with regard to Medicare, and it could throw your retirement finances off course if you accidentally buy into it. Here are some of the biggest misconceptions about Medicare floating around.

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1. Medicare is free

During retirement, the simple act of taking care of your health could lead to huge monthly expenses. And that's partly because Medicare is by no means free.

Though enrollees typically do not pay a premium for Part A, which covers hospital care, Part B, which covers outpatient services, comes with a monthly premium you'll need to either pay on your own or have deducted from your Social Security payments if you're already receiving those benefits. Part D, which covers prescriptions, also comes with a premium you must pay.

But that's not all. You'll also have co-pays, coinsurance, and deductibles to meet under Medicare. So be sure to budget plenty of money for medical expenses once you're all signed up.

2. It doesn't matter when you enroll

Your initial Medicare enrollment window lasts seven months. It begins three months before the month of your 65th birthday, and it ends three months after that month. But delaying your enrollment could end up being a costly mistake.

If you don't sign up for Medicare on time, you'll face a 10% surcharge on your Part B premiums for each 12-month period you could've enrolled but didn't. And penalties could apply for delaying your Part D coverage too long as well. So once you become eligible for Medicare, look into enrolling so you don't end up paying more for life.

3. It doesn't matter which plan you choose

Medicare Parts A and B are universal -- all enrollees get the same coverage. But when it comes to Part D, you have choices. And not reviewing different plan options could mean spending more money on prescriptions than necessary and getting stuck with higher premium costs.

All that said, it's possible to enroll in Medicare Advantage, which is an alternative to original Medicare (meaning Parts A and B, plus a Part D drug plan). But there are plan choices to navigate within the realm of Medicare Advantage, too, so it's important to review your options for coverage and pay attention to the costs involved.

Don't fall victim to misinformation

Many retirees have to tighten their budgets once they stop collecting a paycheck from work. The last thing you want is to plan poorly for healthcare expenses under Medicare and struggle financially. So instead, know how the program works, and read up on some of the costs you might have to grapple with once you enroll.