While Medicare Part A is hospital insurance, Medicare Part B is medical insurance. What's the difference? Part B covers you outside the hospital. It helps cover the cost of medically-necessary services like doctors’ services, outpatient care, and ambulances. Part B also covers some preventive services like flu shots, prostate cancer screenings and mammograms.

Some Other Services all or Partially Covered by Part B Include (Among Others):

• Out-patient surgeries
• Clinical lab services
• Diabetes screenings and supplies
• Durable medical equipment like walkers
• Emergency room services
• Second opinions for surgery
• Urgent care

Almost all of these services and supplies carry a co-payment, usually 20%. Also, Part B has an annual deductible you must pay out of pocket, though it is fairly low.

Unlike Part A, Medicare Part B is not free. You must pay a monthly premium, which is usually automatically deducted from your Social Security check. You can opt out of Part B, but if you decide to enroll after the age of 65, you'll pay a significant penalty in the form of higher premiums forever.