Medigap refers to various private supplemental medical insurance plans sold to Medicare recipients' in the USA that provide coverage for medical expenses not or only partially covered by Medicare.

Medigap's name is derived from the notion that it exist to cover the difference or "gap" between the expenses reimbursed by Medicare and the total amount charged. As of 2006, 18% of Medicare beneficiaries were covered by a Medigap policy

Eligibility:
A person must be enrolled in part A and B of Medicare before they can enroll in a Medigap plan. During the open enrollment period which begins within 6 months of turning 65 or enrolling in Medicare Part B at 65 or older, a person may obtain a Medigap plan on a guaranteed issue basis (i.e. no medical screening required). Outside of open enrollment, the issuing insurance company may require medical screening and may obtain an attending physician's statement if necessary. Medigap insurance is not compatible with other forms of private Medicare coverage, such as a Medicare Advantage plan.

Products available:
Medigap offerings have been standardized by the Centers for Medicare and Medicaid Services (CMS) into twelve different plans, labeled A through L, sold and administered by private companies. Each Medigap plan offers a different combination of benefits. The coverage provided is roughly proportional to the premium paid. However, many older Medigap plans offering minimal benefits will cost more than current plans offering full benefits. The reason behind this is that older plans have an older average age per person enrolled in the plan, causing more claims within the group and raising the premium for all members within the group. Since Medigap is private insurance and not government sponsored, the rules governing the sale and offerings of a Medigap insurance policy can vary from state to state. Some states such as Massachusetts, Minnesota, and Wisconsin require Medigap insurance to provide additional coverage than what is defined in the standardized Medigap plans. Some employers may provide Medigap coverage as a benefit to their retirees.

Drug coverage:
Some Medigap policies sold before January 1, 2011 may include prescription drug coverage, but after that date no new Medigap Plans could be sold with drug coverage. This time frame coincides with the introduction of the Medicare.

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