Medigap plans, also called Medicare Supplement Plans, or Med Supp, provide extra insurance that helps you pay for your Medicare Parts A and B out-of-pocket costs – such as co-insurance and deductibles – which are “gaps” in medical coverage. Medigap plans are purchased through private carriers, though federal and state laws regulate Medigap policies. Medigap policies are only available to people who already have Medicare Part A and B, and should be purchased during your Medigap Open Enrollment Period.