Part B covers services which are considered to be medically necessary for treating a disease or condition. These services include lab tests, doctor visits, durable medical equipment (DME) and preventive services. The monthly premium for Part B is based on your income plus any late enrollment penalties that may apply.
After you have paid an annual deductible, Medicare pays 80% of most Part B services and you pay 20% coinsurance. Most preventive services are covered 100% by Medicare if you get the service from a provider who accepts assignment from Medicare. There is no annual out-of-pocket maximum that limits your cost-sharing for Part B services.