It really depends where you are eating and the service you recieve. As noted in the other answers 15% is the expected ammount. And most cell phones have a feature to figure out what 15% of your check would be. However, if you get really good service you should add a little extra because servers do work for tips their paycheck is very small. Also keep in mind even for bad service it is very tacky not to give a tip at all. You can always leave the tip yet pull the server to the side and let them know what they did wrong. And finally some resturaunts will have a set tip ammount or percentage, places such as this will automatically add the tip to your check. Good Luck and Bon Appetite!
Being an ex-waitress I can tell you that normal tip is 15%. The easiest way is to just double the tax because that usually equals the right amount. If you receive exceptional service then you can always tip more.
I usually tip between 15 and 20 percent. Wait staff makes so little without tips and they put up with a lot from people. If they're good, they deserve 15 to 20 percent. If they are bad, I leave 5 to 10 percent, or horrible and rude: nothing.
I usually tip 20% unless the waiter is rude or really neglectful. If it is a buffet sometimes I only tip like 15% because the waiter doesn't have to do very much.
