When you are setting fees you can do so by setting them at 100%-300% of Medicare allowable. Once your fee is set and you have a cash pay patient you would give them discount off the actual billed amount. I'm assuming you mean for patients you are out of network with? If in network you need to look at your contract, you cannot discount the patient and not give carrier the same discount.
For example: You set fee for 99213 at $200 Your practice financial policy allows for 20% cash discount for those with no insurance or not using their insurance, you would give 20% off the $200.