Several factors like age, health, body type and size, weight, fitness goal and activity level dictate the amount of calories you should eat in a day. Before determining how many calories are needed to gain or lose weight, let’s start with how many calories it takes to maintain your current weight. In order to get a general idea of how many calories you burn in a day, multiply your current weight by the daily amount of energy used: inactive persons should multiply weight times 14 to 16 calories; somewhat active 16 to 18 calories; and extremely active 18 to 20 calories.

110 lbs. somewhat active: 110 x 18 = 1980 calories

180 lbs. inactive: 180 x 14 = 2520 calories

250 lbs. extremely: 250 x 20 = 5000 calories

If you want a more precise number of how many calories to consume in a day, you must take into consideration the constant rate at which calories are burned at a state of rest. This is called your basal metabolic rate (BMR). Combining your BMR with amount of work you body does when not at rest (computer work, lifting weights, cooking, jogging etc.) will give you your Total Daily Energy Expenditure (TDEE). Everyone’s BMR and TDEE varies: it takes less fuel to maintain a moderately active, petite forty-something female than it does an active, voracious teenage male. Here’s how to determine your BMR and TDEE:

Males: 66 + [6.23 x weight (lbs.)] + [12.7 x height (in.)] – [6.8 x age (years)]

Females: 655 + [4.35 x weight (lbs.)] + [4.7 x height (in.)] – [4.7 x age (years)]

BMR + Work = Total Daily Energy Expenditure [TDEE]

If you BMR is 1500 calories a day and you spent 45 minutes on a treadmill and burned 500 calories and needed another 400 calories to complete an eight-hour work day at the office, then your TDEE would be 2400.

The Harris Benedict Formula calculates daily calorie intake by multiplying your BMR by your activity level. The more active you are, the higher the number you multiply your BMR by:

Little to no exercise |
BMR x 1.2 |

Light exercise (1-3 times per week) |
BMR x 1.375 |

Moderate exercise (3-5 times per week) |
BMR x 1.55 |

Heavy exercise (6-7 times per week) |
BMR x 1.725 |

Extremely heavy exercise (more than 7 times per week + physical job) |
BMR x 1.9 |

But of course we all have different body types, and one shortcoming of the Harris-Benedict Formula is that it treats all bodies the same. This formula fails to consider leaner, more muscular individuals by underestimating the number of calories needed. Similarly, and on the opposite end of the spectrum, the amount of calories needed for overweight individuals is overestimated. The Harris-Benedict Formula is most beneficial to the average person trying to maintain a current acceptable body weight of shed a few pounds.

The Katch-McArdle formula uses a different equation to calculate your BMR. It does not take sex into consideration, but readily adjusts to varying body types. If you know your lean body mass percentage (or your percentage of body fat), then you can apply this information to get a more accurate BMR.

For example:

A 170 lb. person with 20% body fat would have 136 lbs. of lean muscle mass and 34 lbs. of fat: [170 lbs. x 20% body fat= 34] , then [170 lbs. – 34= 136 lbs. of lean muscle mass]

Then calculate your BMR by using the following equation:

370 + [9.79759519 x lean muscle mass] = BMR

370 + [9.79759519 x 136] = 1702.47295

Once you have established your BMR using the Katch-McArdle formula, apply the same numbers used in the Harris-Benedict table to incorporate the amount of weekly physical activity to get your TDEE.

Little to no exercise |
BMR x 1.2 |

Light exercise (1-3 times per week) |
BMR x 1.375 |

Moderate exercise (3-5 times per week) |
BMR x 1.55 |

Heavy exercise (6-7 times per week) |
BMR x 1.725 |

Extremely heavy exercise (more than 7 times per week + physical job) |
BMR x 1.9 |

Below are a few more ways for you to figure out just how many calories your body needs to maintain your current weight.

Step 1: Multiply your body weight by 10.

Step 2: Determine what your overall activity level is - very active=add 60% - 80% to your RMR; moderately active=add 40% - 60%; generally sedentary, add 20% - 40%.

For example, if you weigh 150-pounds and consider yourself to be moderately active, then the following equation - 1500 + (1500 x 50%) = 1500 + 750, or 2250 calories - is would apply to you. Be sure to enter your particular numbers into this equation in order to find out exactly what your caloric intake should be each and every day.

This equation is one of the most accurate methods to use when it comes to figuring out you’re your particular caloric needs should be for the day.

Step 1: First convert pounds to kilograms by dividing by 2.2.

Step 2: Next, convert the inches to centimeters by multiplying by 2.545. For the most part, all moderately active people are generally advised to consume about 1.5 to 1.7 times the calculated resting metabolic rate (RMR).

Once you know what the recommended amount of daily calories are for you, you can easily figure out how to adjust this number in order to either lose or gain weight. Given that 3,500 calories is equal to 1 pound, you are able to take your daily allotment of calories and figure how many less or more calories you will need to get you to the weight that's just right for you!

When counting calories to lose weight, there are a few key pieces of information to know before starting a plan.

- Don’t try to lose weight too fast. Fad diets claiming you will lose more than 2 pounds per week are usually unhealthy, and your body is quick to reclaim the lost weight once off the diet. Eliminating 500 calories from your body per day, whether achieved by eating less, exercising more, or a combination of the two, will result in losing one pound per week. A pace for healthy weight loss is two pounds per week.
- Second, should your calorie counter determine eating less than 1000-1200 calories per day for a woman and 1300-1500 for a man, forgo what the calorie counter says and consume the aforementioned minimums. Eating less can sometimes cause the body to slow your metabolic rate; the slowing of the metabolism is sometimes referred to as “starvation mode.”

Whether improving your self-image or overall health, people who lose weight feel better. Starving your body will leave you feeling just the opposite: sluggish, run-down, and sickly. So remember to stay informed of what you eat and stay active!

http://www.cordianet.com/calculator.htm

http://www.multivitamin.co.uk/bmr-results/

http://www.bmi-calculator.net/bmr-calculator/harris-benedict-equation/

http://www.roth.net/Articles/Misc/Calories/

http://healthylifejournal.org/articles/what-are-calories-and-how-do-they-affect-you/

Matthew Johnson (Google+) is a certified personal trainer, nutrition expert and an on-line fitness consultant that started ChangingShape.com back in 2001.

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