To determine daily calorie needs (DCN), add your basal metabolic rate (BMR) and calories required for daily physical activity. 

DCN = BMR + daily activity calories

The basal metabolic rate or BMR is the amount of energy required, in the form of calories, to sustain a one’s daily involuntary bodily functions such as circulation, respiration, temperature maintenance, hormone secretion, nerve activity, and new tissue synthesis. Basal metabolism consumes the majority of calories per day for functioning. There are numerous equations to determine basal metabolism.  A quick and easy estimate of BMR is

Men: kg body weight x 24 = cal/day
Women: kg body weight x 22 = cal/day
(lbs/2.2 = kg)

When determining your daily caloric needs, it is important to determine an activity level.  When you move and exercise, the body requires additional calories to fuel the activity.  Even if you are mostly sedentary, the body still needs calories beyond that which is required for BMR.  The category of activity level will be broken down into sedentary (20-35%), light activity (35-50%), moderate activity (50-65%), and heavy activity (65-100%). 

Sedentary: You sit down or stand still most of the day.
Light: You move around some of the time.  For example –  a school teacher, who does no additional exercise, falls into this category. 
Moderate:  Your occupation is in the light category and you add regular exercise weekly, or your occupation requires moderate physical work such as a golf or yoga instructor.  Moderate activity includes hoeing and weeding, gardening, recreational bicyling, skiing, and tennis.
Heavy: Your occupation is physically demanding such as a roofer or carpenter or you get 10+ hours of high intensity exercise per week. This includes fast jogging, basketball, soccer,  advanced ballet, and body-building.

Now let’s try some examples.  Jill weighs 130lbs and is in the light activity category.  Jack weighs 200lbs and is in the heavy activity category. 
First, we must change pounds to kg.
Jill – 130lbs/2.2 = 59kg        Jack – 200lbs/2.2 = 91kg

Next, find BMR using the quick and easy equation above.
Jill (female):  59kg x 22 = 1,298 cal/day      Jack (male): 91kg x 24 = 2,184 cal/day

Then, calculate activity energy expenditure.
Jill (light activity 35-50%): 1,298 cal/day x 0.35 = 454 cal      1,298 cal/day x 0.50 = 649 cal
Jack (heavy activity 65-100%): 2,184 cal/day x 0.65 = 1,420 cal   2,184 cal/day x 1.00 = 2,184 cal

Finally, plug numbers into DCN = BMR + daily activity calories

Jill, female, 130lbs, light activity
DCN = 1,298 BMR + 454 cal = 1,752 cal/day     1,298 BMR + 649 cal = 1,947 cal/day
DCN = 1,752 – 1,947 cal/day

Jack, male, 200lb, heavy activity
DCN = 2,184 BMR + 1,420 cal = 3,604 cal/day    2,184 BMR + 2,184 cal = 4,369 cal/day
DCN = 3,604 – 4,369 cal/day

When determining your daily calorie needs, it is important to remember that this is an estimate.  There are additional factors which can alter both energy expenditure and energy needs such as the ratio of lean body mass to fat mass.  Certain prescription medications can speed up or slow down basal metabolism. Pregnancy and illness can also change basal metabolism. 

Determining your daily calorie or energy needs is a great first step to losing weight or gaining weight. If you want to lose weight, consume enough calories for your basal metabolism, and either take in less calories for activities or increase your activity level.  If you want to gain weight, consume enough calories for your basal metabolism, and either consume more calories for activities or decrease activity level.   Remember to adjust your BMR periodically while you are losing or gaining weight.  Please consult your physician before changing your diet or starting an exercise program.