With Medicare Open Enrollment in full swing, you may still have questions you need answered before you sign up. Making healthcare decisions can be difficult, so five of the most commonly asked questions about signing up are answered below to help you navigate the process.

About 10,000 people turn 65 every day, and along with that milestone comes a challenge: You need to get up to speed on the many ins and outs of Medicare. There's a lot at stake. You have to pick supplemental insurance to fill Medicare's coverage gaps, and you might have to switch to less-expensive versions of some medications. If you don't sign up by the deadline or you make other mistakes, you could end up with lifetime penalties, denied claims or big bills you shouldn't have to pay.

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Every day, my in-box is filled with questions from readers about the nuances of Medicare. The following frequently asked questions concerning signing up will help you navigate the system and deal with tricky issues.

Q: Do I need to sign up for Medicare, or will I be enrolled automatically?

A: If you signed up for Social Security before age 65 (eligibility for full benefits currently begins at age 66), you will automatically be enrolled in Medicare parts A and B and receive your card three months before your 65th birthday. Part A covers hospitalization and is generally premium-free; Part B covers outpatient care, such as doctors' visits, X-rays and tests, and costs $134 a month for people who enroll in 2017 (or more for high earners).

Everyone else needs to take steps to enroll -- or face a lifetime late-enrollment penalty (unless you're still working and have employer coverage; see below). Go to www.socialsecurity.gov to sign up anytime from three months before until three months after you turn 65 (your "initial enrollment period"), even if you are waiting to file for Social Security benefits.

Q: I'm still working. Do I need to sign up?

A: That depends on the size of your company. If you or your spouse (if you're covered by your spouse's insurance) is still working for a firm with 20 or more employees, the employer's insurance is your primary coverage, and Medicare is secondary and can fill any gaps in coverage. You aren't required to sign up for Medicare at 65, and you won't have a late-enrollment penalty as long as you sign up within eight months of leaving your job and losing work-based coverage (or losing coverage under your spouse's insurance).

If you work for a large employer and are happy with its coverage, you may decide to delay signing up for Part B. (Many people still sign up for Medicare Part A at 65.) But the rules are different if you work for a company with fewer than 20 employees. In that case, Medicare generally becomes your primary coverage at age 65, and you need to sign up for Part A and Part B while you're still working. Some small employers negotiate with insurers to keep employee coverage primary for workers after age 65, but this is unusual; get it in writing from your boss before you delay signing up.

Also note that you can't delay signing up for Part A if you're already receiving Social Security benefits and were automatically enrolled in Medicare--even if you're still working.

Q: I have a health savings account at work. Can I still contribute to my health savings account after I turn 65?

A: Yes, as long as you haven't enrolled in Medicare. If you are able to delay signing up for Medicare parts A and B (see above), you can continue contributing to an HSA. Before you decide, determine whether the HSA's tax breaks, any employer contributions and other benefits are more valuable than the premium-free Part A coverage.

Q: I have retiree health insurance. Do I need to sign up for Medicare at age 65?

A: Unless you or your spouse is still working and has current employer coverage, you should sign up for both Medicare Part A and Part B at 65. Retiree coverage can fill gaps in Medicare (which would otherwise require Medigap and Part D policies or a Medicare Advantage plan), but it's secondary to Medicare after age 65, and it may not kick in at all if you don't sign up for Medicare. Federal retiree coverage is an exception; it remains your primary coverage if you don't sign up for Medicare, but you will pay a penalty if you decide to sign up for Part B later.

Q: What's the penalty for not signing up?

A: You'll have to pay a late-enrollment penalty of 10 percent of the Part B premium for every year you should have had coverage. The penalty applies as long as you receive Medicare benefits. If you miss the initial enrollment period or the eight-month window after you or your spouse stops working, you can only sign up from January through March in any year for coverage to begin July 1.

If you have additional questions about Medicare, check out some of our other resources:

This article is written by Kimberly Lankford from Tribune Health Columnists and was legally licensed via the Tribune Content Agency through the NewsCred publisher network. Please direct all licensing questions to legal@newscred.com.