For an Original Medicare enrollee, the excess charge is the difference between a doctor’s fee for service and what Medicare Part B has approved as payment for that service.
The excess charge only applies if the doctor doesn’t “accept assignment” with Medicare, but has not opted out of Medicare altogether. In other words, they’re a non-participating provider.
When a non-participating provider bills Medicare, their approved amount is only 95 percent of what Medicare would approve for a participating provider (ie, a provider who does accept assignment, agreeing to accept Medicare’s normal approved amount as payment in full). That 95 percent is paid partially by Medicare, and partially by the patient in the form of coinsurance (or by the patient’s supplemental coverage, if they have it). But then the non-participating provider is allowed to charge up to 15 percent more, on top of the amount that Medicare approves for the service. This additional amount is called an excess charge. It’s either paid by the patient or by the patient’s supplemental coverage (Medigap plans F and G cover Part B excess charge).
Because Medicare pays non-participating providers less than participating providers, the excess charge amounts to less than 115 percent of the normal Medicare-approved amount, as explained here.
Some states prohibit non-participating providers from billing Medicare patients for excess charges, or limit the amount to something less than 15 percent.