You use energy no matter what you're doing, even when sleeping. The BMR Calculator will calculate your Basal Metabolic Rate (BMR); the number of calories you'd burn if you stayed motionless for a day.
If you've noticed that every year, it becomes harder to eat whatever you want and stay slim, it is because your BMR decreases as you age. Likewise, skipping meals in hopes of losing weight also lowers your BMR. However, a regular routine of cardiovascular exercise can increase your BMR, improving your health and fitness when your body's ability to burn energy gradually slows down
Based on your BMR value, and considering your activity level, you can work out how many calories you need to gain weight or lose weight. You would multiply your BMR by a scale between 1.2 (for little to no exercise) to 1.9 (for extremely active/physical job and sports) to work out your actual daily expenditure, then to gain weight add 500cal or to lose weight subtract 500cal. These are simply guidelines and not an exact science.
Body Fat Calculator
This calculator gives you an idea of what your Body Fat percentage is. These are not definitive values are and are used for simple guidance,
How much Body Fat are you carrying? Find out if you are in the healthy range. First, your body fat percentage is simply the percentage of fat your body contains. If you weigh 140 pounds and are 10% fat, it means that your body consists of 14 pounds fat and 126 pounds lean body mass (bone, muscle, organ tissue, blood etc)
A certain amount of fat is essential to bodily functions. Fat regulates body temperature, cushions and insulates organs and tissues and is the main form of the body's energy storage.