Medicare covers more than 54 million beneficiaries, around 77% of whom are happy with their insurance. Yet this vital social program doesn't cover every single beneficiary's needs. If you're covered by Medicare, or will be soon, it's important to understand both its benefits and its limitations. 

Stethoscope lying on pile of money

Image source: Getty Images.

Medicare Part A pays for inpatient hospital care, skilled nursing care, hospice care, and home healthcare. Part B covers 80% of most routine care, but many Medicare recipients eventually experience a health need Medicare won't cover. It helps to know what kinds of things Medicare won't pay for and plan ahead for costs.

Here are four big expenses Medicare won't pick up the tab for -- and some suggestions on how to afford this care. 

1. Long-term care 

Medicare defines long-term care as "a range of services and support for your personal care needs." While most people think of long-term care as the type of care you receive in a nursing home, it can also include home healthcare and even adult day-care services. If you need assistance with daily activities like bathing, using the bathroom, or eating, then you need long-term care -- and about 70% of retirees can expect to need it at some point in their lives.

In 2016, a shared room in a nursing home cost an average of $6,844 monthly. A private room would bump your monthly bill to $7,698 . Meanwhile, the average retirement income for Americans 65 and older is just over $2,645 a month -- not nearly enough to pay for a nursing home. And you can't count on Medicare to pay the difference.

Medicare Part A covers nursing care facilities only if skilled nursing care (like changing surgical dressings) is necessary . If you need custodial care -- the routine care that sends most seniors to nursing homes -- Medicare will not provide coverage. 

Similar limitations exist for other types of long-term care, like home healthcare. Optional Medicare Advantage Plans also limit coverage for long-term care, so buying an Advantage plan won't help. 

How can you cover long-term care costs?
Planning ahead is of vital importance. One option is to buy long-term care insurance. Premiums run an average of $3,560 annually for a couple in their 60's to buy a policy that pays up to $150 daily ; not quite enough to fully cover the average $220 daily expense for a nursing home.

Medicaid is a primary source of payments for nursing home care. Qualifying for Medicaid requires spending down assets because Medicaid provides long-term care coverage only for people with few resources. Working with an attorney to protect assets can sometimes help you preserve wealth and get covered.

Taking advantage of any VA benefits for nursing home care may also be helpful for qualifying former military members and their families. 

2. Dental care

Medicare does not cover routine visits to the dentist, nor will it pay for common treatments like root canals or fillings. Seniors who require dentures are also on their own, as are Medicare beneficiaries who need serious procedures like oral surgery for gum disease. 

Medicare pays for dental treatments only if those treatments are medically necessary for a patient to undergo other covered treatment. If you must get a tooth extracted before undergoing heart surgery, Medicare pays for the extraction. 

More than 60% of seniors visit the dentist annually , and average costs exceed $685 per person for routine annual care. Specialist care costs significantly more. Close to a quarter of all seniors aged 65 to 74 have dental disease classified as "severe," so taking care of your teeth is costly but essential. 

How can you cover dental care costs?
Many Medicare Advantage (aka Medicare Part C) plans provide dental coverage. These are optional plans from private insurers that supplement traditional Medicare, and they can expand coverage in many other ways besides just covering dental visits.

Be sure to shop carefully for coverage, paying attention to premiums, the type of dental benefits provided, and the network of covered providers.

If you don't want a Medicare Advantage plan with dental coverage, look into programs offering discounts on dental care or talk with local dentists about cash discounts or payment plans. Dental schools can also provide lower-cost cleanings and treatments. 

3. Eye exams and glasses

More than 90% of people in their 50s require glasses or contact lenses. Annual eye exams are required to update your prescription and check for serious conditions like cataracts. Unfortunately, traditional Medicare will not pay for exams or corrective eyewear.

The average cost for a new-patient eye exam could reach as much as $200, while repeat exams are around $128. Specialized care costs more, and glasses with nice frames, protective coatings, and specialty lenses can cost $350 or more. Not having the right prescription can cause headaches and dizziness, and it can be dangerous while driving. You cannot afford to skip out on eye care. 

How can you cover the costs of eye exams?
Medicare Advantage plans may cover eye exams and basic frames. Glasses or contacts are often not fully paid for.

You can often find much better prices for eyewear online than you'd find in a physical store. For example, Eye Buy Direct often offers specials like "buy one, get one" glasses, while Zenni Optical has eyewear options starting at just $6.95 and including features like anti-scratch coating. Shipping for an entire order is just $4.95.   

You'll need to submit your lens prescription and sizing information to the seller. Look at your current pair of glasses to find the eye size, bridge size, and temple length. Frames Direct also has a step-by-step guide, with pictures, to help you get these specs for yourself if you can't find them on your current glasses.

If you must pay out-of-pocket for your eye exam, look into discount options including optician services provided at big-box stores like Sam's Club, Costco, and Wal-Mart.

Many opticians also run specials, such as offering a free exam if you purchase glasses. Shop around carefully and consider the total costs of the exam and eyewear. Always check review sites to confirm the quality of local discount providers. 

4. Hearing aids

Close to a quarter of all seniors aged 65 to 74 suffer from disabling hearing loss; this number jumps to 50% of the population aged 75 and up. Acting quickly to obtain a hearing aid is important because waiting too long forces your brain to relearn certain sounds, making it more difficult for you to adjust to a hearing aid.

Medicare won't cover your costs, which can be substantial. The average price of a single hearing aid is $2,300, while hearing aids with advanced features can cost more than $20,000. 

How can you cover the cost of hearing aids?
Medicare Advantage will often pay at least part of the cost of a hearing aid, and the VA provides a no-cost hearing aid for most eligible veterans.

If you don't have coverage, some Costco stores offer free screenings and hearing aids priced as low as $500 to $1,500. According to Consumer Reports, buying online could also save as much as $2,000, but you should shop around to find a trusted source. It may also be possible to purchase pre-owned hearing aids at a substantial discount.

When you make your purchase, avoid buying more hearing aid than you need by making sure your audiologist knows the specific hearing limitations you want to correct.

By research all of the ways to make your healthcare spending affordable, you can minimize your out-of-pocket spending on services that Medicare doesn't cover. This means you'll have more cash to spend on spoiling the grandkids, traveling, or whatever it is that brings you joy in retirement.

The Motley Fool has a disclosure policy.