Health Maintenance Organization (HMO) plans: One of the most popular types of managed-care plans, this type of Medicare Advantage plan comes with a provider network that you must use to be covered by the plan (with the exception of medical emergencies). If you use non-network providers, you may have to pay the full cost for your care. You’re also required to have a primary care physician; if you need to see a specialist, you’ll need to a get a referral from your primary care doctor first.

Before 2003 Part C plans tended to be suburban HMOs tied to major nearby teaching hospitals that cost the government the same as or even 5% less on average than it cost to cover the medical needs of a comparable beneficiary on Original Medicare. The 2003-law payment framework/bidding/rebate formulas overcompensated some Part C plan sponsors by 7 percent (2009) on average nationally compared to what Original Medicare beneficiaries cost per person on average nationally that year and as much as 5 percent (2016) less nationally in other years (see any recent year's Medicare Trustees Report, Table II.B.1). 

However, you may have to wait up to six months for coverage if you have a pre-existing health condition. The insurer through which you buy your Medigap policy can refuse to cover out-of-pocket costs for pre-existing conditions during that period. After six months, the Medigap policy must cover the pre-existing condition. The exception to this rule is if you buy a Medigap policy during your open enrollment period and have had continuous "creditable coverage," or a health insurance policy for the six months before buying a policy. The Medigap insurance company cannot withhold coverage for a pre-existing condition in that case.
Medicare Part B premiums are commonly deducted automatically from beneficiaries' monthly Social Security checks. They can also be paid quarterly via bill sent directly to beneficiaries. This alternative is becoming more common because whereas the eligibility age for Medicare has remained at 65 per the 1965 legislation, the so-called Full Retirement Age for Social Security has been increased to 66 and will go even higher over time. Therefore, many people delay collecting Social Security but join Medicare at 65 and have to pay their Part B premium directly.
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