Short Answer: Medicare Supplement (Medigap) plans are a kind of private health insurance that helps pay your out-of-pocket costs if you have Original Medicare (Part A & B) coverage. There 10 plan types (each denoted by a letter); each letter policy is required by law to offer the same benefits, no matter what state you live in or which insurer you buy the plan from.*
This chart will help you easily compare Medicare Supplement plans. (Click the chart to enlarge it)
For each plan in the chart above, the percentage represents what the Medicare Supplement plan covers. You’ll need to cover the rest of the cost for the service, if your plan covers less than 100% of a benefit.
You’ll notice that Plans C and F are the only ones that cover the Medicare Part B (medical insurance) deductible. As of January 1, 2020, however, you’ll no longer be able to enroll in Plan C or F, in accordance with a 2015 law passed by Congress that prohibits the sale of Medicare Supplement plans that cover the Part B deductible. The law will only affect those who are newly eligible, however—if you’re eligible and sign up for Plan C or F before January 1, 2020, you’ll be grandfathered in and able to keep your plan.
*Massachusetts, Minnesota and Wisconsin do not have the same standardized plans as the rest of the country.