Most HMOs (Health Maintenance Organizations) charge a monthly premium in addition to the Medicare Part B premium and copayments for services you get. Copayments for some services, such as hospital stays, mental health care, medical equipment and cancer treatment, may be high.

Every HMO is different and your out-of-pocket costs will vary depending upon the HMO you join and the services you receive. HMOs must have a limit on out-of-pocket costs. You are protected from very high costs if you use a lot of medical care or expensive treatments. The maximum out-of-pocket cost for most HMOs in 2018 is $6,700. If you use doctors and hospitals that are not in the HMO’s network or you see many providers, your costs might be higher. You cannot buy Medigap supplemental insurance to fill the gaps in HMO coverage. 

HMOs may raise premiums, cut benefits, or stop offering Medicare coverage altogether, at the end of the calendar year.

HMOs may charge a higher premium if they offer Medicare drug coverage (Part D). The premiums may also be higher if they offer coverage of services that are not covered by Original Medicare, such as dental and vision care.