Medicare Supplement Insurance · Also called: Medicare Supplement, guaranteed issue, Medigap open enrollment
Private insurance that pays some or all of the deductibles and coinsurance Original Medicare leaves to you. Plans are standardized by letter. It cannot be combined with Medicare Advantage.
You have a one-time six-month Medigap open enrollment period that starts the first month you are both 65 or older and enrolled in Part B. During it an insurer must sell you any policy it offers at its standard price, regardless of health.
After that window, insurers in most states may use medical underwriting and can decline you or charge more. This makes the initial choice between Medigap and Medicare Advantage hard to reverse later.