This is NOT a simple topic.
Usual and Customary(U&C, or UCR) (sometimes referred to as Reasonable and Customary (R&C) refers to the base amount that third-party payers (including insurance carriers and employers) generally use to determine how much will be paid for reimbursable services. This amount is calculated based on review of prevailing charges of OTHER physicians in a particular service and area(geographical area) UCR/R&C is set at the 80-90th percentile of that amount (collected in data .. I think the most recent prevailing data is from 1994, don't quote me on that)
Now you can try to figure this out but it would be much easier to bang your head on the wall.
With NON par and U&C/R&C remember that the amount OVER U/C and R&C is patient responsibility. IF your provider is PAR, then it's fee schedule and the amount over fee schedule and minus patient OOP is your adjustment (write off)
With amounts OVER U&C you can bill the patient. But..before you do that there are a few things you can do..
First with any major procedure (set a policy in the office of for example procedures over $500) send the carrier a per-determination of benefits. For a Pre-d, you want to send the procedure codes that will be anticipated and billed and the amount of the procedure. Sometimes carriers will take these via fax, call first and find out their procedure.
The carrier will then give you a written YES or NO that the fee is within the U&C amount and how much is OVER U&C, or that the fee is within U&C. For example if you give them a procedure and price of $500 they will either tell you it's $-- OVER U&C or the fee is within U&C. They don't want physicians inflating charges if the fee is within by telling you what the U&C is if it's more than your fee for that procedure.
From that point your patient should know what their OOP will be. Later on if complications arise or they cut the fee more than they should have you can file an appeal. The carrier will tell you what they need to determine if additional monies are to be paid out. Sometimes with a large U&C cut the provider can get a bit more out of the carrier with either notes or an operative report. You want to include any additional information NOT sent with the original claim that justifies the added fee.
Again, keep in mind the amount OVER U&C is considered patient responsibility and is a part of their COST sharing so NOT billing them can be a violation of their policy. Providers should always make reasonable attempts to collect patient OOP.