Upwards of 67 million Americans receive healthcare insurance through Medicare. Signed into law by President Lyndon B. Johnson in 1965, Medicare covers a wide range of hospital and physician expenses and prescription drugs.

The government makes Medicare available to permanent residents and citizens at age 65; younger people with specified disabilities and end-stage renal disease can also apply. The Social Security Administration processes enrollments and deducts the premium from its monthly benefits.

Medicare consists of four components. Medicare Part A pays for inpatient hospital services, treatment in mental hospitals, skilled nursing and home health care, and hospice. Part B applies to physicians’ treatments, either in their offices or a hospital or other facility. It also pays for ambulance services, lab tests, and physical and rehabilitative therapy.

Part C, or Medicare Advantage, moves through private insurers; it includes expenses not included in Parts A and B, such as dental and vision care and hearing aids. Benefits can also apply to prescription drugs. Recipients pay the private insurers an extra premium. Part D pays for medication expenses, which private companies administer. However, both plans do not cover all drugs.

Medicare enrollment is automatic for people receiving Social Security benefits for at least four months before their 65th birthday; otherwise, they can self-enroll for seven months after that date.