It was calculated for me. I have a slow metabolism and little muscle mass and my maintenance is around 2200.
How many calories would you eat?
Ok your maintenance is 2200. Eat 2200.
Then create a surplus by doing cardio, weight training etc.
Do cardio 5-6 times a week. Cycle your calories 2 days 2200, 2 days 1800, 1 day 2500 etc
If you are counting calories now then you are in a good position. Eat 6 meals high protein, moderate carb and only healthy fats. Stick with starchy carbs earlier in the day, moving to fibrous carbs later on. You could try Layne Nortons method of 3.5+ hours between meals but that doesn't work for some people(i.e. people can't wait that long etc)