fitness calculator
You use energy no matter what you're doing, even when sleeping. Jim White's Fitness Calculator will calculate your Basal Metabolic Rate (BMR)—the number of calories you'd burn if you stayed in bed all day—and combine that with an activity level to determine your total daily energy expenditure (calories).
Once you know the number of calories needed to maintain your weight, you can easily calculate the number of calories you need to eat and/or expend in order to lose weight.