How many calories needed each day to lose weight depends on a number of factors and can vary from individual to individual.
What Is a Calorie?

When considering how many calories needed each day to lose weight, you hear the term calorie bandied about, but most people have a really nebulous idea of what a calorie actually is.

A calorie is a unit of food energy. Six nutrients contain calories. Carbohydrates and proteins have four calories per gram. Fats are more energetically dense, and have nine calories per gram. Alcohol has seven calories per gram. Other sources of calories include organic acids (such as acetic acid and lactic acid) and polyols (sugar alcohols such as Mannitol, Xylitol and Glycerol).

Calories and Weight Loss

One of the basic tenants of weight loss is that you need to burn more calories than you eat in order to lose weight. While this is true, the process is a little more complex than that simple statement indicates.

Calories - energy units - are burned by your body as energy. There is, however, a limit to the amount of calories your body utilizes as energy. This amount varies from person to person based upon a number of factors including your basic metabolic burn rate, the amount of lean body mass you have, and your activity level. Other chemical and hormonal factors may also affect how many calories your body burns each day, but they are beyond the scope of this article and are best discussed with a nutritionist or physician.

Any calorie consumed that your body does not convert to energy is stored as body fat.

Basal Metabolic Rate
Your basal metabolic rate is your minimal caloric burn rate. These are the calories you need just to exist and support bodily functions such as respiration, heart beat and digestion to name a few. This is an important number to consider when determing how many calories needed each day to lose weight. It is never advisable to have a daily caloric intake that falls below this basal metabolic rate (BMR). There are a number of methods that can be used to calculate BMR ranging from the very scientific which is done in a doctor's office to an estimation that will work well for most people who are trying to get a handle on how much to eat. To get a general idea of your BMR, use this BMR calculator. This is the lowest amount of calories you should EVER eat unless directed otherwise by a physician.

Lean Body Mass
In general, the more lean body mass you have, the more calories your body will burn. Lean body mass is everything in your body that is not fat including muscles, bones, water and organs. Your lean body mass to body fat ratio is also referred to your body composition. There are a number of ways to measure body composition, including skin fold calipers and hydrostatic weighing. Most body composition calculations need to be done by an expert who has been trained in body composition. Skin caliper measurements are usually the least expensive method.

Activity Level
The more active you are, the more calories you will burn. Activity level includes more than formal exercise. It also includes how sedentary or active your job is, and whether you fidget a lot or sit still. There is a good basic equation that takes your activity level into account and recommends caloric intake based upon how active you are. This equation is called the Harris-Benedict equation. You can use a Harris-Benedict calculator to calculate your daily caloric needs.

How Many Calories Needed Each Day to Lose Weight?

Your individual answer will depend on the two numbers you derived - your BMR and your Harris-Benedict number. Since you need to burn more calories than you take in, a good rule of thumb is to take your Harris-Benedict calculation and subtract between 300 and 500 calories from that number. This, then, would be your required daily caloric intake for weight loss.

Eating Below Your BMR

Never eat below your BMR number, because your body will begin to convert your lean body mass to energy. This, in turn, decreases your lean body mass (even though your weight is dropping), which decreases your basal metabolic rate. This can become a vicious cycle that traps many dieters, who find they can eat less and less and need to exercise more and more to even be able to maintain their weight loss.

Increasing Your Body's Ability to Burn Calories

Is the number of calories you can eat and still lose weight alarmingly low? You can increase your body's ability to burn calories. There are two ways you can do this. First, you can increase your lean body mass through strength training. Secondly, you can increase your activity level. If you significantly increase your activity level, you will need to recalculate your caloric needs so that you can continue healthy weight loss that sacrifices minimal lean body mass.