You can tip more than 15% if you wish, but is properly figured on the amount before tax.
If you are comped a meal or use a coupon, figure the tip on the amount before the comp or coupon, that is, as if there was no comp or coupon.
Travel tips:
http://members.aol.com/ajaynejr/travel.htm
Once a restaurant automatically added in a tip figuring it on the amoutn after tax. I complained and insisted that they correct it even though I would have voluntarily left a larger tip if they did not add it in automatically. In retrospect I think I overreacted.
[This message has been edited by AllanJ (edited 08-03-2002).]