Medicare Supplements are policies sold by private insurance companies that help pay for some of the costs that Original Medicare does not cover (including copays, deductibles, and coinsurance). Medicare Supplements are also referred to as Medigap coverage.
All Medigap policies are standardized by law. There are several different types of Medicare Supplements, and they are identified by letters A through N. “Each standardized Medigap policy must offer the same basic benefits, no matter which insurance company sells it. Cost is usually the only difference between Medigap policies with the same letter sold by different insurance companies” (Section 2, page 9 of the Department of Health and Human Services Medigap Handbook).
To put this more simply, a Plan F covers you the same way, no matter which company you purchase it from; the only difference is how much you pay monthly for the coverage. For example, Plan F with Company ABC costs you $175/mo, but Company XYZ offers Plan F for $130/mo. That means that Company XYZ can offer the EXACT SAME COVERAGE for a better price than company ABC.
Remember, these plans are all standardized by law. Supplement plans with the same letter from different companies have the same coverage by law; the only difference is the monthly premiums that you pay.
Medicare Supplement plans that cover both the Part A and Part B deductible (Supplement Plan F and Plan C) will no longer be available to newcomers to Medicare as of January 1, 2020.
*Note that Medigap (Medicare Supplement) policies in Massachusetts, Minnesota, and Wisconsin are standardized in a different way.*