What is a customary gratuity?

We often get asked what is considered a "good tip" to leave for a therapist? Generally a client can follow these guidelines: 15% for a "Satisfactory" service, 20% for "Excellent" service and 20 plus% for "Superior" service. We are appreciative of any gratuities given and they are optional and at the client's discretion. We thank you for your continued business.