The number of calories you need to eat per day is determined by a number of factors, including your age, height, activity level and whether you want to maintain your current weight or lose a few pounds.
Define Your Body Type
The first step in determining the right eating plan for your body is to define your frame. Are you athletic? Are you slender? An easy way to check this is to wrap your hand around your wrist, till your thumb and middle finger touch. If they overlap, you have a small frame. If they just touch, you have a medium frame and if they don't touch at all, you have a large frame. This is important in deciding where in the continuum you should be. A woman in her twenties, who is 5'5", may have a weight range of 53kg-59kg. If she is small framed, she may feel more comfortable at the lower end of the range. If she is has a larger frame, than the higher end may suit her better.
Determine Your Activity Level
Take a careful look at your weekly exertion to determine how much activity you are doing each day. If you have a cubicle job and don't exercise at all after work, then you are sedentary. If you do light exercise at least 2 or 3 times a week, then you are lightly active. If you do moderate exercise 4 or 5 times a week then you are moderately active. And if you exercise heavily 5 or 6 times a week, then you are very active. A rule of thumb is the more activity you do, the more calories you need to consume to maintain your current weight and energy level.
Determine Your Goals
Decide whether you are comfortable with your weight or would like to lose weight. If you want to lose weight, subtract the number of calories per day you are comfortable going without, making sure you eat no less than 1200 calories per day. Be careful to subtract appropriate calories for any exercise you are doing.
The last step is to input your information into a calorie calculator to determine the actual caloric intake for your age and height. The Mayo Clinic has a very simple, easy to use, calculator. You will need to have your activity level and body frame information handy.
Know Which Calories to Eat
Every calorie counts. Don't waste your day's allowance on empty calories. Foods that are low calorie and low-fat might look good if you want to satisfy a craving, but you may be more likely to overeat if you don't go for the real thing in moderation. If you're craving chocolate, go for a real chocolate bar, but eat the small snack-sized one. You want the majority of your calories to be whole grains, fruits, vegetables and lean proteins. Eat dairy and starches in moderation.
If you have existing medical conditions, like diabetes or low blood sugar, then your diet and exercise plan needs to be monitored by a trained physician.