Medicare Supplement insurance plans also commonly known as Medigap, assist with covering deductibles and coinsurance that Original Medicare does not. About 80% of your medical expenses are covered by Medicare; the remaining 20% must, of course, be covered by you. Depending on your level of coverage, the supplement plan will pay the difference. A Medicare Supplement enrollment plan is available to you if you have Original Medicare Parts A and B. Your six-month open enrollment window will start the month you turn 65. Your Medicare Part B effective date will then start a once-in-a-lifetime Open Enrollment period. Being disabled for 24 months also qualifies you for Medicare, and the Open Enrollment period is decided by the Part B effective date. You cannot be turned down for coverage due to a pre-existing condition or condition at the time of open enrollment for Medicare Supplements. Some states offer a plan or plans to people under 65 who are eligible for Medicare for reasons other than age, although not all states permit health underwriting. Any doctor or hospital that accepts Medicare patients may be used if you have Medicare Supplement coverage.