Because basic Medicare coverage has limitations, many people purchase supplemental insurance policies to cover any gaps. These policies —called Medicare Supplement or “Medigap” policies — are sold by private health insurance companies.

The types of health care costs that Medicare Supplements cover include copayments, coinsurance and deductibles. However, they don’t usually cover long-term care, vision, dental, private-duty nursing, hearing aids or eyeglasses.

Enrollees must have Medicare Part A and Part B, but cannot have a Medicare Advantage Plan, which is different because that type of policy provides actual Medicare benefits. As the name says, Medicare Supplement policies only supplement the Original Medicare benefits.

A Medicare Supplement policy only covers one person; if a spouse wants Medigap coverage, they have to buy a separate policy.