This calorie calculator uses the Mifflin St Jeor Equation which appears to be the most accurate formula for a basic calculator that takes your BMR (basal metabolic rate) and your activity levels into account. For those that know their LMB (lean body mass) we will be adding another calculator that uses LBM shortly, as this is much more accurate. In the mean time, our BMR and Calories page tells you how to do the calculation using your lean body mass as well as other information that you may wish to read up on first. If you're calculating your LBM using bodyfat scales, keep in mind that body fat scales are not always accurate because they rely on hydration. A person who is dehydrated or carrying less fluid due to being in ketosis, ( common on a low carb diet), will show a higher body fat percentage then they actually are.
These calorie calculators are only a guide, a persons BMR can be different even when weight, age, height, sex and lean body mass match. Wikipedia explain this quite well.
Please keep these factors in mind, remember weight loss isn't a race and that lowing your calories too much can be detrimental: Very low calorie diet risks. Keep in mind, you don't always have to lower calories as the deficit can also be achieved through increasing activity levels which include many benefits. Resistance exercise will also increase your metabolic rate through adding muscle mass and when dieting doesn't allow for this, it can also help you maintain your metabolism by helping to preserve muscle mass. Feel free to play around with the activity level in the BMR/Calorie calculator to see the difference various levels can make.
The Macronutrient Calculator allows you to quickly work out your PFC (protein, fat and carbohydrate) amounts in grams by entering your daily calorie limit and the PFC ratio that you would like to use.