99% of the time I will tip 20% of the total. There's only been a handful of times that I tipped 15% but they have to do a lot to cause that. Once a friend and I only tipped 10% cause the person waiting on us had pretty much dropped off our food, which was wrong, walked by our table to see if we needed anything once (which was almost immediately after we got our correct food), and when we asked to get a refill on our drinks, they forgot and we had to ask another waitress to get our drinks. Oh, and we were the only people in the restaurant at the time, so it wasn't like the person waiting on us was busy or anything.