Medicare supplement insurance, or Medigap, is an additional health insurance policy you can buy from a private insurer to help pay some of the costs not covered by Original Medicare, including deductibles, coinsurance and health care if you travel outside the U.S. Medigap plans don’t cover long-term care, prescription drugs, dental, vision, hearing aids or private nursing care. There are 10 types of Medigap plans available in most states. Plan F and Plan G are the 2 most comprehensive and the most popular. Premiums depend on gender, ZIP code and tobacco use and for Plan F can range from around $120 per month to over $400. You must have Original Medicare to purchase a Medigap policy. Medigap is not compatible with Medicare Advantage — you would purchase one or the other.