A Medicare supplement (Medigap) insurance, sold by private companies, can help pay some of the health care costs that Original Medicare doesn't cover, like copayments, coinsurance, and deductibles.
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 health care costs. Then your Medigap policy pays its share.

A Medigap policy is different from a Medicare Advantage Plan. Those plans are ways to get Medicare benefits, while a Medigap policy only supplements your Original Medicare benefits.

Six things to know about Medicare Supplement policies:

1. You must have Medicare Part A and Part B.
2. If you have a Medicare Advantage Plan, you can apply for a Medigap policy, but make sure you can leave the Medicare Advantage Plan before your Medigap policy begins.
3. You pay the private insurance company a monthly premium for your Medigap policy in addition to the monthly Part B premium that you pay to Medicare.
4. A Medigap policy only covers one person. If you and your spouse both want Medigap coverage, you'll each have to buy separate policies.
5. Any standardized Medigap policy is guaranteed renewable even if you have health problems. This means the insurance company can't cancel your Medigap policy as long as you pay the premium.
6. Some Medigap policies sold in the past cover prescription drugs, but Medigap policies sold after January 1, 2006 aren't allowed to include prescription drug coverage. If you want prescription drug coverage, you will need to join a Medicare Prescription Drug Plan (Part D).

Medigap policies don't cover everything:

Medigap policies generally don't cover long-term care, vision or dental care, hearing aids, eyeglasses, or private-duty nursing