A 20% tip is expected at full service, sit down restaurants. At buffets or self serve, 10-15% is acceptable depending on what services are rendered by the waitstaff. If you get your own drink, your own refills, stack and clear your own plates--go toward the 10% figure. If the waitstaff actually gets your drink order and checks frequently for refills, or if you order bar service, 15% is more like it. Regarding food delivery (i.e., pizza) if the delivery fee does not include a tip, 10% is adequate. Frankly even if it does, I usually will ante up a few extra dollars for the delivery person. Hope this helps...