I have a question. We are a Psychologist office that accepts Medicare insurance. I am trying to figure out the co pay formula or rules when the patient only has Medicare and no secondary insurance. Our Billed amount is 130.00, our allowed amount is 89.67, Medicare pays 44.83, are we allowed to charge our patients for the remainder amount that Medicare doesnt pay(44.84)? Someone told me that we are only allowed to charge 20% of the allowed amount, then someone else said 20% of the charged amount and yet another biller said charge the full amount that Medicare doesnt pay??? Thanks!!