Medicare Part A and Part B, also known as Original Medicare or Traditional Medicare, cover a large portion of your medical expenses after you turn age 65. Part A (hospital insurance) helps pay for inpatient hospital stays, stays in skilled nursing facilities, surgery, hospice care and even some home health care. Part B (medical insurance) helps pay for doctors' visits, outpatient care, some preventive services, and some medical equipment and supplies. Most folks can start signing up for Medicare three months before the month they turn 65.

It's important to understand, however, that Medicare Part A and Part B leave some pretty significant gaps in your health-care coverage. To that end, here's a closer look at what isn't covered by Medicare, plus information about supplemental insurance policies and strategies that can help cover the additional costs, so you don't end up with unexpected medical bills in retirement.

1.    Prescription Drugs

Medicare doesn’t provide coverage for outpatient prescription drugs, but you can buy a separate Part D prescription-drug policy that does, or a Medicare Advantage plan that covers both medical and drug costs. (Some retiree health-care policies cover prescription drugs, too.) You can sign up for Part D or Medicare Advantage coverage when you enroll in Medicare or when you lose other drug coverage. And you can change policies during open enrollment season each fall. Compare costs and coverage for your specific medications under either a Part D or Medicare Advantage plan by using the Medicare Plan Finder.

2.    Long-Term Care

One of the largest potential expenses in retirement is the cost of long-term care. The median cost of a private room in a nursing home was nearly $97,500 in 2017, according to the Genworth Cost of Care Study; a room in an assisted-living facility cost $45,000, and 44 hours per week of care from a home health aide cost $49,000. Medicare provides coverage for some skilled nursing services but not for custodial care, such as help with bathing, dressing and other activities of daily living. But you can buy long-term-care insurance or a combination long-term-care and life insurance policy to cover these costs. See Medicare Rules for Home Health Care for information about Medicare’s strict rules for covering home health care.

3.    Deductibles and Co-Pays

Medicare Part A covers hospital stays, and Part B covers doctors’ services and outpatient care. But you’re responsible for deductibles and co-payments. In 2018, you’ll have to pay a Part A deductible of $1,340 before coverage kicks in, and you’ll also have to pay a portion of the cost of long hospital stays -- $335 per day for days 61-90 in the hospital and $670 per day after that. Be aware: Over your lifetime, Medicare will only help pay for a total of 60 days beyond the 90-day limit, called “lifetime reserve days,” and thereafter you’ll pay the full hospital cost.

Part B typically covers 80% of doctors’ services, lab tests and x-rays, but you’ll have to pay 20% of the costs after a $183 deductible in 2018. A medigap (Medicare supplement) policy or Medicare Advantage plan can fill in the gaps if you don’t have the supplemental coverage from a retiree health insurance policy. Medigap policies are sold by private insurers and come in 10 standardized versions that pick up where Medicare leaves off. If you buy a medigap policy within six months of signing up for Medicare Part B, then insurers can’t reject you or charge more because of preexisting conditions.

Medicare Advantage plans provide both medical and drug coverage through a private insurer, and they may also provide additional coverage, such as vision and dental care. You can switch Medicare Advantage plans every year during open enrollment season.

4.    Most Dental Care

Medicare doesn’t provide coverage for routine dental visits, teeth cleanings, fillings, dentures or most tooth extractions. Some Medicare Advantage plans cover basic cleanings and x-rays, but they generally have an annual coverage cap of about $1,500. You could also get coverage from a separate dental insurance policy or a dental discount plan. Another alternative is to build up money in a health savings account before you enroll in Medicare (this would require that you carry a qualified high deductible healthcare plan, see this link for more on creating a Health Savings Account (HSA); you can use the money tax-free for medical, dental and other out-of-pocket costs at any age (bear in mind that you can’t make new contributions to an HSA after you sign up for Medicare).

5.    Routine Vision Care

Medicare generally doesn’t cover routine eye exams or glasses (exceptions include an annual eye exam if you have diabetes or eyeglasses after having certain kinds of cataract surgery). But some Medicare Advantage plans provide vision coverage, or you may be able to buy a separate supplemental policy that provides vision care alone or includes both dental and vision care. If you set aside money in a health savings account before you enroll in Medicare, you can use the money tax-free at any age for glasses, contact lenses, prescription sunglasses and other out-of-pocket costs for vision care.

6.    Hearing Aids

Medicare doesn’t cover routine hearing exams or hearing aids, which can cost as much as $3,000 per ear. But some Medicare Advantage plans cover hearing aids and fitting exams, and some discount programs provide lower-cost hearing aids. If you save money in an HSA before you enroll in Medicare, you can also use that tax-free for hearing aids and other out-of-pocket expenses.

7.    Medical Care Overseas

Medicare usually doesn’t cover care you receive while traveling outside of the U.S., except for very limited circumstances (such as on a cruise ship within six hours of a U.S. port). But medigap plans C through G, M and N cover 80% of the cost of emergency care abroad, with a lifetime limit of $50,000. Some Medicare Advantage plans cover emergency care abroad. Or you could buy a travel insurance policy that covers some medical expenses while you’re outside of the U.S. and may even cover emergency medical evacuation, which can otherwise cost tens of thousands of dollars to transport you aboard a medical plane or helicopter.

How to Look Up What Is and Isn't Covered by Medicare

To look up Medicare’s coverage rules and other types of care and procedures, go to Medicare.gov/coverage and use the “Is my test, item or service covered?” tool.