When you're enrolled in Medicare, you have access to a wide range of benefits from the federal government. You also have a seemingly uncountable number of coverage details and rules to sort through — and that can make understanding health insurance feel overwhelming.

The last thing you need when you're trying to obtain health care in retirement is to be overrun by information or stressed out over how you'll pay for health insurance. This guide to health insurance for people with Medicare is designed to be a one-stop source for the basics, such as what Medicare covers and doesn't cover and how you can get help paying for any uncovered health care needs.

How Medicare Covers Health Care Needs

There are two basic Medicare coverage options: Original Medicare, which includes Part A (hospital insurance) and Part B (medical insurance); and Medicare Advantage, also known as Part C, which is a comprehensive alternative that covers parts A and B and often includes Part D, the Medicare prescription drug plan.

If you are enrolled in Original Medicare, you can go to any doctor, health care provider, hospital or health facility in the U.S. that participates in Medicare and is accepting new Medicare patients.

If you are enrolled in a Medicare Advantage plan, you'll need to see an in-network health care provider to get the lowest cost. Some Medicare Advantage plans don't offer any coverage for out-of-network care, and some plans require a referral to see a specialist.

What Medicare Covers

Each part of Medicare covers specific services. In general, Part A covers:

• Inpatient hospital care.
• Short-term skilled nursing facility care and nursing home care.
• Inpatient mental health care.
• Hospice care.
• Home health care.

Part B covers medically necessary services and preventive services, including:

• Ambulance services.
• Durable medical equipment.
• Inpatient and outpatient mental health.
• Health screenings, such as mammograms, diabetes screenings, cancer screenings and cardiovascular disease screenings.
• Annual wellness visits, flu shots and immunizations.

What Medicare Doesn't Cover

But Medicare doesn't cover everything. It usually doesn't cover:

• Prescriptions, unless you're enrolled in a Part D plan.
• Long-term care.
• Eyeglasses and eye exams.
• Dentures and most dental care.
• Cosmetic surgery.
• Acupuncture.
• Hearing aids and hearing exams.
• Routine foot care.

The Medicare website offers a full, searchable list of what is and isn't covered. If Medicare doesn't cover the service you need, you'll have to pay for it yourself or purchase supplemental insurance.

What Is Medicare Supplement Insurance?

Medicare pays for a lot of the costs of the services and supplies it covers, but it doesn't pay for everything — including deductibles and copayments, which can quickly get costly. One way to pay for some of the things that Medicare doesn't cover is to purchase a Medicare Supplement insurance policy — a private insurance plan that helps pay for some out-of-pocket health care costs that Original Medicare doesn't cover. Medicare Supplement insurance plans are also called Medigap plans, because they bridge gaps in Medicare coverage. Note, too, that Medicare Supplement policies cover just one person. If you and your spouse both want supplemental coverage, you'll need separate policies.

Like Medicare, Medicare Supplement insurance plans have some coverage limitations.

What Medicare Supplement Insurance Covers

The coverage and benefits you'll receive will depend on which of 10 available standardized Medicare Supplement policies you choose, but they all share one benefit: Every policy covers 100% of your Part A coinsurance and up to 365 additional days of hospital costs after your Medicare hospital insurance benefits are exhausted.

Beyond that, the main differences in Medicare Supplement plans are in how they treat other health care costs, such as:

• Part B coinsurance and copayments.
• Deductibles for Medicare parts A and B.
• Part A hospice coinsurance and copayments.
• Skilled nursing facility care coinsurance.
• Part B excess charges (i.e., charges above the Medicare-approved amount).
• Blood transfusions.
• Foreign travel emergencies.

(If you live in Massachusetts, Minnesota or Wisconsin, the Medicare Supplement policies are standardized in a different way, but each still covers the entirety of the Part A coinsurance.)

Some Medicare Supplement policies pay all or a portion of these expenses. Some don't cover any costs at all. Some come with out-of-pocket limits; others don't. Review the different types of plans available to you — and make sure you're comparing the same types to one another — when you're shopping for supplemental health insurance.

The Medicare website explains in greater depth the coverage each Medicare Supplement plan type provides.

What Medicare Supplement Insurance Doesn't Cover

Medicare Supplement insurance usually doesn't cover:

• Long-term care.
• Vision care.
• Eyeglasses.
• Dental care.
• Hearing aids.
• Private-duty nursing.
• Prescription drugs.

How Can I Get Supplemental Health Insurance?

You can enroll in a Medicare Supplement policy from any insurance company that's licensed to sell Medicare in your state. You can search for insurers in your area on the Medicare website.

To be eligible to purchase Medicare Supplement insurance, you must have Medicare parts A and B. You cannot obtain a supplemental policy if you're enrolled in a Medicare Advantage plan. However, if you are planning to switch from that plan to Original Medicare, you can apply for a Medicare Supplement policy in advance and ask to have the coverage start when your Medicare Advantage enrollment ends.

Your right to purchase Medicare Supplement insurance is guaranteed during your open enrollment period, a one-time six-month period that begins on the first day of the month in which you're 65 or older and enrolled in Medicare Part B. If you're under 65, you might not be able to buy the supplemental policy you want — or any Medicare Supplement policy — until you turn 65, though some states offer open enrollment periods for applicants under 65.

During open enrollment, insurance companies can't deny your application, charge you higher premiums or, in most cases, delay the start of your coverage based on your health status. They can, however, impose a waiting period of up to six months on coverage if you have specific preexisting health conditions. Some insurance companies will sell you a Medicare Supplement policy outside of your open enrollment period, but others may deny coverage or, if they approve it, delay the coverage because of your health.

Once you obtain a Medicare Supplement insurance policy, it's guaranteed renewable, regardless of how your health changes.

The Right Health Insurance Coverage Means Peace of Mind

As health care costs continue to change, both within the market and as you age, it's important to have a plan for how you'll cover those costs during your retirement years. Medicare covers some of those expenses, but not all of them, and the coverage gap can leave you on the hook depending on your specific needs.

As this guide to health insurance for people with Medicare shows, Medicare Supplement insurance could lower your out-of-pocket costs and give you the security of knowing you'll be able to afford the health care you need to live a fulfilling lifestyle during retirement.