The mathematics of calorie balance are simple: To keep your weight at its current level, you should remain at your daily caloric maintenance level. (bodybuildingforyou.com)
You will need to calculate your daily caloric maintenance number and then add 400 calories to that if you want to put on more muscle. (fitnessandpower.com)
Sedentary lifestyles of Western Civilization have lead to very low caloric maintenances with respect to our ancestors. (anymanfitness.com)