Here is the equation.
Make sure your daily total amount of input calories is > your daily total of calories you burn.
If you are a 20 year old 207 lb male for example, you should be eating around no more than 1600-2000 calories per day if you want to lose weight. If you want to lose weight faster than eat 1400 - 1600 calories a day and add exercise. Do not eat less than 1400 because your body will go into starvation mode from lack of calories and you will gain weight as your body starts storing all the fat because it thinks you are starving