The maximum will vary greatly - depending on your goals. Total calories for maintenance, gaining muscle or losing fat will all be different. Your lifestyle, metabolism and daily activities will all effect how many calories you burn daily. You can get a pretty good idea of how many you burn using fitday.com. They have an 'activities' tab that lets you enter your daily activities - at the top of the page you'll see calorie information for BRM based on your age, sex and weight and another for lifestyle (this will depend on what you enter when you register) The total of all 3 will give you an idea of just how many calories you burned that day. Just as a benchmark, I average about 3400 calories for BMR, lifestyle and activities a day. So theoretically I could eat 3000 calories and not gain any fat.

HTH
Nat