On its face, weight loss seems simple: As long as you burn more calories than you eat, you should shed pounds. But almost anyone who has tried to reclaim her waist can point to weeks or months when it doesn't seem to work that way. Here are four vital statistics for helping you meet your weight-loss goals.

Daily calorie count
Once you know your Resting Metabolic Rate [will link to: Managing Your Weight: Calories In vs. Calories Out], you will need to account for physical activity to determine the total number of calories you expend each day. Here, an equation is the most practical method to gauge your calorie burn. Multiply your RMR by the appropriate activity factor:

If you are sedentary (little or no activity) - RMR x 1.2
If you are slightly active - RMR x 1.375
If you are moderately active (moderate exercise/sports 3-5 times a week) - RMR X 1.55
If you are very active - RMR x 1.725

The number you get represents the minimum number of calories you need to eat daily to maintain your current weight. Researchers believe that you have to burn roughly 3,500 calories to lose a pound of fat, so to lose 1 pound a week, a safe rate of weight loss, you'd need to diet or exercise your way to a 500-calorie deficit every day.