Medicare Supplement policies are supplemental health insurance policies sold by private insurers, designed to fill some of the “gaps” in health coverage provided by Medicare. Although Medicare covers many health care costs, you still have to pay certain coinsurance and deductible amounts, as well as paying for services that Medicare does not cover.
Generally, you must be enrolled in the original Medicare Parts A and B before you need to purchase a Medicare Supplement insurance policy. Other types of health insurance coverage, such as Medicare Advantage, other Medicare health plans, Medicaid, or employer-provided health insurance, do not work with Medicare Supplement policies.