I've been reading some of the Biggest Loser books and one of the suggestions is to separate your calories at the beginning of the day by allocating calories for each meal (3) and snacks (2)
For example if your total calories per day are 1,400 then divide by 4 which will give you 350 calories for each meal. Divide the 350 to give yourself 175 calories for each snack.
1400/4 = 350
350/2 = 175
They recommend if you go over your allocated calories per day, then exercise to burn off those extra calories.
It's always wise to talk to your doctor first to calculate a safe number of calories per day. MyFitnessPal will calculate your personal daily calorie count and it's a great way to keep track of both calories and nutrition. - the basic app is free to use.