Serving about 55 million Americans in 2015 with its Part A and/or Part B coverage, Medicare is a program most of us need to know about. After all, most of us will rely on Medicare benefits to some degree once we reach age 65. You may know that Part A covers hospital-related expenses and Part B covers healthcare provider services, but there's a good chance that you don't fully appreciate many of the benefits included in Medicare. Let's fix that.

Overview

First, though, let's review some Medicare basics. Medicare is a government program created in 1965 that offers healthcare coverage to people aged 65 and up, and younger folks with certain disabilities or permanent kidney failure. Part D is optional coverage for prescription drugs, while Part C refers to Medicare Advantage plans, which are offered by private insurers, and are designed to offer at least as much coverage as traditional Medicare.

You're eligible for Medicare at age 65, and can sign up anytime within the three months leading up to your 65th birthday, during the month of your birthday, or within the three months that follow. If you fail to enroll during this time, you can always enroll during the "general enrollment period," which is from January 1 through March 31 of each year. (If you're still working, with employer-provided healthcare coverage at age 65, or are serving as a volunteer abroad, you can delay enrolling in Medicare without penalty.)

Most people will automatically be enrolled if they're already receiving Social Security benefits during their enrollment period. But everyone else faces a significant danger: Being late to sign up for it can result in more expensive premiums for the rest of your life. Specifically, your part B premiums -- which cover medical services, but not hospital services -- can rise by 10% for each year that you were eligible for Medicare but didn't enroll.

Medicare benefits

What Medicare benefits are offered by Part A and Part B? Generally, most services that are considered "medically necessary" are covered -- with some exceptions. For the most part, routine care of vision, hearing, and teeth is not covered, nor is long-term nursing-home care. Annual wellness checkups are covered, as are many important screenings -- free of charge. For example, free screens include mammograms and Pap tests, along with screenings for heart disease, colorectal cancer, prostate cancer, depression, glaucoma, hepatitis C, alcohol misuse, HIV, STDs, diabetes, and osteoporosis.

Below are a bunch of specific Medicare benefits that you may not know about, and might want to. Most are either provided free of charge, or have the patient paying 20% of the Medicare-approved cost (with a deductible applying):

Abdominal aortic aneurysm screening: If you're deemed to be at risk and your doctor orders this screening.

Ambulance services: These are covered in many cases when deemed necessary.

Artificial limbs and eyes: These are covered when ordered by a doctor.

Breast prostheses: Both external breast prostheses (including a post-surgical bra) and surgically implanted breast prostheses are covered after a mastectomy.

Chiropractic services: If manipulation of the spine by a chiropractor or other qualified provider is deemed medically necessary to correct a subluxation, it's covered.

Continuous Positive Airway Pressure (CPAP) therapy: If you're diagnosed with obstructive sleep apnea, Medicare will cover some of the costs of a CPAP machine and its supplies.

Durable medical equipment (DME): These include blood sugar monitors and diabetic testing strips, suction pumps, walkers, wheelchairs, crutches, home oxygen equipment, commode chairs, nebulizers, infusion pumps, and hospital beds, among other items.

Hepatitis B shots: If you're at high or medium risk of hepatitis B, shots are covered.

Home health services: These include intermittent skilled nursing care, physical therapy, speech-language therapy, and occupational therapy.

Hospice care: If you're deemed to have a life expectancy of no more than six months, you can qualify for free hospice care.

Laboratory tests: Medically necessary clinical diagnostic laboratory tests ordered by your doctor or practitioner are covered, usually free of charge.

Mental healthcare: Both inpatient and outpatient mental healthcare services are covered, to some degree.

Obesity screening & counseling: This is available free for those who qualify by having a body mass index (BMI) of 30 or more.

Physical therapy/occupational therapy/speech-language pathology services: These are covered, with yearly limits applying to services from most outpatient providers.

Second opinions: If you are having non-emergency surgery, Medicare will sometimes cover the cost of getting a second opinion from a different doctor -- and, on occasion, even a third opinion if the first two differ.

Smoking cessation counseling: This is covered both for those who have and have not yet been diagnosed with a tobacco-related illness.

Telehealth: This is where patients consult and interact with healthcare providers remotely and electronically, and it's a growing practice. Medicare covers some telehealth services when the patient is at a health-service facility.

Transplants: Medicare covers doctor services for certain organ transplants.

Growing old is not an exciting prospect, and the looming costs of healthcare as we get older can be scary, but Medicare is there to cover many costs we incur -- in full or in part. When it comes to Medicare benefits, it's helpful to know what is and isn't covered in order to make maximum use of Medicare, and save more money.