How many calories does my body burn while doing NOTHING?? Well kiddo, that is called your BMR

Your Basal Metabolic rate is the amount of energy that your body "burns" in a 24-hour period while doing absolutely nothing. If you were seated on your couch, watching TV for 24 hours, you would burn the equivalent of your BMR in calories. It's possible to estimate your BMR from a formula. Obviously, this wont be 100% accurate, but it gives you a pretty good idea of what your body needs to function. These formulas are:

MEN: BMR = 66 + (13.7 x weight in kg) + (5 x height in cm) — (6.8 x age)

WOMEN: BMR = 655 + (9.6 x weight in kg) + (1.7 x height in cm) — (4.7 x age)

Let's take, for example, a 29-year-old man, 5'9" (175 cm) and 207 pounds (94 kg):

BMR = 66 + (13.7 x 94) + (1.7 x 175) — (6.8 x 29)

BMR = 66 + 1287 + 297 — 197

BMR = 1453 calories

This man would burn 1453 calories in a 24-hour period, while doing absolutely nothing.

Depending on your daily activity, your actual Daily Energy Expenditure (DEE), or the amount of calories you burn in a day, will vary. You can estimate this amount by multiplying your BMR by an "activity" factor.

1.0 = sedentary (do nothing all day but eat potato chips and watch TV)

1.2 = very light activity (desk job, no training, some walking)

1.4 = light activity (no training, job might require some light physical labor)

1.6 = moderate activity (most of us: a physically undemanding job, but training on a regular basis)

1.8 = high activity (daily training plus a somewhat physically active job or lifestyle)

2.0 = very high activity (twice-a-day training, sports + training. or training + a very demanding job)

So in our example, if our 1453-calorie subject is moderately active, his DEE would be around 2324 calories per day (1453 x 1.6). This means that he needs to consume 2324 calories per day, just to maintain his physical status quo (neither gaining nor losing weight).

You should remember, again, that these are only approximate figures. It's better than guessing, but it's only really precise with "normal" individuals. If you're a mesomorph (naturally very muscular and lean), for example, this formula tends to underestimate your caloric expenditure by around 10%. It's still a workable formula, though it might require some tinkering and tweaking.

Another way to establish your DEE is to record everything you eat for a week, then calculate your caloric intake. If you neither gained nor lost any weight in that 7-day period, then you basically ate at your DEE. This method, although a bit more precise, can be a real pain in the ass, so most people should stick to the calculation and adjust their caloric intake depending on how their body is responding.