Learn the daily calories needed to achieve your fitness goals. Your calorie requirements should be determined by your genetics, weight, activity level and fitness goals. There is a minimal caloric need for your body to function properly. Calorie needs is also slightly different for males and females.
A larger individual will generally require more calories than a smaller individual. A 150 pound male may only require 1400 calories a day while a 250 pound guy may require 1800 per day just to maintain enough energy to get through the day. The activity level of a person also determines how many daily calories are required. A female the exercises 5 days a week and jogs will require more energy than a person that lives a sedentary lifestyle. Your fitness goals also are a determinate in your calorie needs. If you are trying to lose weight, you may want to lower your calorie intake. If a male is trying to pack on muscle mass, he may decide to increase his calorie intake. You must be careful not to go to low because this can have a negative effect on your body functions.
If your primary goal is to gain muscle, eating right is a key component. Here are 6 tips for healthful weight gain.
Knowing how many calories you should consume varies with each individual. You must feed your body enough calories for it to function properly. Factors such as weight, height, gender and activity level are used to determine your calorie needs. Here's a handy tool below to give you a rough calorie needs estimate.
The Harris Benedict Equation is a formula that uses your BMR (Resting Energy Expenditure) and then applies an activity factor to determine your total daily energy expenditure (calories). The only factor omitted by the Harris Benedict Equation is lean body mass. Remember, leaner bodies need more calories than less lean ones. Therefore, this equation will be very accurate in all but the very muscular (will underestimate calorie needs) and the very obese (will overestimate calorie needs).
To get a rough estimate of how many calories you need in a day to maintain your present weight, multiply your weight by 13, if sedentary, and by 15, if moderately active. You need to add more calories for rigorous exercise.
To lose or gain weight, subtract or add 500 calories through diet and exercise. For example to lose about a pound a week, decrease your calorie intake by 250 calories and increase the calories you burn off through exercise by 250. Walking one mile briskly in 15 minutes burn approximately 100 calories.
Here's a sample showing you how to use the Harris Benedict Equation to determine the amount of calories you burn while resting.
WARNING: Use this formula only as an estimate.
Download Medium size (17" by 11") Harris Benedict formula chart.
Example 1
Susan is 45 years old; she weighs 245 pounds and is 5 foot 5 inches tall. She works the type of job where she sits for most of the day. Susan does not exercise, ever. How many calories is Susan burning while at rest?
Step 1
Plug Susan's weight, height, and age into the formula below for women to find her BMR.
English BMR Formula 
Women: BMR = 655 + (4.35 x weight in pounds) + (4.7 x height in inches)  (4.7 x age in years)

BMR=655 + (4.35 x weight in pounds) + (4.7 x height in inches)  (4.7 x age in years).
BMR=655 + (4.35 x 245) + (4.7 x 65)  (4.7 x 45)
BMR=655 + 1065.75 + 305.5  211.5
BMR= 1814.75
Step 2
Determine Susan's activity level using the chart below
Harris Benedict Formula 
To determine your total daily calorie needs, multiply your BMR by the appropriate activity factor, as follows:
* If you are sedentary (little or no exercise): CalorieCalculation = BMR x 1.2
* If you are lightly active (light exercise/sports 13 days/week): CalorieCalculation = BMR x 1.375
* If you are moderately active (moderate exercise/sports 35 days/week): CalorieCalculation = BMR x 1.55
* If you are very active (hard exercise/sports 67 days a week): CalorieCalculation = BMR x 1.725
* If you are extra active (very hard exercise/sports & physical job or 2x training): CalorieCalculation = BMR x 1.9

Step 3
Plug numbers into the formula
Since Susan is sedentary, you would multiply her BMR X 1.2
Plug in the appropriate numbers
Susan's calories burned while at rest = SUSAN'S BMR X 1.2
Susan's calories burned while at rest = 1814.75 x 1.2 = 2177.7
Susan burns approximately 2177.7 calories a day at rest
Example 2
If Susan decided to exercise and burn 600 calories how many TOTAL calories would she burn?
Step 1
Plug numbers into the formula below:
Susan's calories burned resting + amount of calories burned exercising.
Susan burns 2177.7 calories resting. If she burns an additional 600 calories exercising Susan would burn 2177.7+600=2877.7
Susan's total calories burned is 2877.7
If Susan wants to shed excess weight for that day she would have to eat less than 2877.7 calories.
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