Original Medicare pays for many, but not all, healthcare services and supplies. Medicare Supplement Insurance policies, sold by private companies, can help pay some of the health care costs that Original Medicare doesn't cover, like copayments, coinsurance, and deductibles. Medicare Supplement Insurance policies are also called Medigap policies.
Some Medigap policies also offer coverage for services that Original Medicare doesn't cover, like medical care when you travel outside the U.S. If you have Original Medicare and you buy a Medigap policy, Medicare will pay its share of the Medicare-approved amount for covered healthcare costs. Then, your Medigap policy pays its share. You have to pay the premiums for a Medigap policy.