In business, a budget collapses a huge amount of detail, the individual transactions, into a small collection of numbers: how much money is allocated to various general purposes. In planning meals, all the multitude of foods and the infinite variety of meals are similarly reduced to a single number: calories per day. To plan meals, it's essential to know how many calories per day you're trying to eat. Where does that number come from?
As you gain more and more experience monitoring and controlling your weight, you'll collect enough information to know precisely how many calories your own body needs per day. Until then, you can start with guidelines for people about like you. Based on your height, frame size, and sex look up the calories burned per day in the tables on pages and . Pick a number in the middle of the range given. For example, Dietin' Doris, five foot four in her bare feet with an average build, would start with a calorie target of 1770. (The range in the table runs from 1574 to 1967, and the average of these numbers is (1574+1967)/2=1770.)
This target assumes Doris' goal is maintaining her present weight. If she wants to lose or gain weight, it must be adjusted based on the daily calorie shortfall or excess she intends. To lose weight at the rate of one pound per week, Doris should eat 500 fewer calories per day than she burns. (Thus, over a week she'll end up 3500 calories shy and hence burn off 3500 calories of fat: one pound.)
Subtracting the calorie cutback, 500, from the number she burns gives the number she can eat per day. Her calorie target is thus 1770-500=1270 calories per day.