They are not interchangeable
Medicare is federal health insurance, mainly for people 65 or older and certain people with disabilities. Other programs may pay with it, after it, or instead of it for some services. Guessing from a friend’s story is how people skip Part B or drop coverage they still need.
Medi-Cal (California’s Medicaid)
Medi-Cal is based mainly on income, resources, and California rules. Some people have Medicare and Medi-Cal together (often called dual eligible). That can mean help with Medicare costs, and in some ZIP codes Dual Special Needs Plans. Having Medicare does not automatically mean you have Medi-Cal.
VA, TRICARE, or FEHB
Military, veteran, and federal-employee coverage is one article, not a second copy of this page. Medicare with VA, TRICARE, or FEHB is the checklist. This map does not say who pays first.
Read the details that match you
Medi-Cal questions stay on the Medi-Cal article. VA, TRICARE, and FEHB stay on the checklist above. Print the worksheet that matches. This website cannot say who pays first on a claim.