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Aug 26 / Jeremy & Kim

Weight Loss Calculator – BMI, BMR, and Daily Calorie Needs

There are a lot of ways to calculate the number of daily calories you need in order to lose weight.   If you have tried to do some research online then you may have gotten confused by all of the acronyms and options out there.  Should you calculate your BMR or your BMI and what do they mean?  How do you calculate your body fat percentage?  How much body fat should you have anyway? If you are curious about what this all means and how to do these calculations then keep reading.  We have you covered. We will describe the purpose and meaning behind each acronym and calculation and we will take all the work out of it by providing an easy-to-use online calculator.

All-in-One Weight Loss Calculator:

We’ll start by giving you the online weight loss calculator in case you are here to just get your measurements and move on, but we encourage you to read the rest of this post so that you know what these numbers mean and how you can use these number to lose weight.

Plug your information into the weight loss calculator above as accurately as possible and then click calculate. By looking at your results you will have taken your first steps toward achieving your fat loss goals.  If you are looking for more information on how to burn fat and get in shape then check out the posts under the category: Mapping Your Route to Fat Loss.

Body Mass Index (BMI)

The Body Mass Index is one of the most common methods of determining if someone is of a healthy weight.  This is unfortunate as it is not necessarily a very reliable or accurate measure of someone’s true body composition. We will discuss why it is unreliable in a minute.

The BMI calculation attempts to determine a person’s mass relative to their size and then makes a judgment as to whether or not that person’s mass is healthy for their size.  To make this determination BMI uses a simple equation:

Body Weight /Height2 (kg/m2)  

For example a man who weighed 79 kg (about 174 lbs) and was 1.8 m (about 5’11”) would have a BMI of 24 (79 ÷ 3.24).  This falls at the upper end of what the BMI classifies as a ‘normal’ weight.

Here is the official BMI classification chart:


BMI is often rightfully criticized for its limitations.  The reason for this is that the calculation does not account for age, sex, or body composition.  It only considers height and mass.  It does not, for example take into consideration that muscle weighs more than fat and people with a decent amount of muscle mass often find themselves as being ranked overweight according to the BMI.


[This is Brad Pilon of Eat Stop Eat explaining some of the limitations of the BMI]

Basal Metabolic Rate (BMR)

The Basal Metabolic Rate (BMR) is an extremely helpful number in helping to determine how many calories someone should aim to consume when trying to lose weight.  The BMR calculates the amount of calories your body will burn in a 24 hour period at a rested state.

For those that are interested, here is the formula:

English Formula (Inch and Pound):

Men: BMR = 66 + ( 6.23 x weight ) + ( 12.7 x height ) – ( 6.8 x age in year )
Women: BMR = 655 + ( 4.35 x weight ) + ( 4.7 x height ) – ( 4.7 x age in years )

Metric Formula (Cm and Kg):

Men: BMR = 66 + ( 13.7 x weight ) + ( 5 x height ) – ( 6.8 x age in years )
Women: BMR  = 655 + ( 9.6 x weight ) + ( 1.8 x height ) – ( 4.7 x age in years )

This means that our man above who weighed 174 lbs and was 5’11” tall would have a BMR of about 1,845 if he was 30 years old.  This means that this man would burn 1,845 calories in a 24 hour period without having to move a muscle.

We highly recommend calculating your BMR and then using that number as the basis for determining your average daily caloric goal.  For example, if the man above was hoping to lose weight then we would recommend that he subtract 500 from his BMR.  This would mean that his average caloric intake goal would be 1,345.  This may sound severe, but you can read more about how to accomplish this in our post Rapid Weight Loss Diet Program.

Total Daily Calorie Needs (TDCN)

The BMR can also used as the basis for determining your total daily calorie needs in order to maintain your weight.  These formulas were first put forward by James Arthur Harris and Francis Gano Benedict in 1919 and are now referred to as the Harris-Benedict equations.  The equation asks you to define your activity level and then offers a multiplier of your BMR to determine the number of calories you need to maintain your weight.

Activity Level:

Sedentary (little or no exercise): BMR x 1.2
Lightly active (light exercise/sports 1-3 days/week): BMR x 1.375
Moderately active (moderate exercise/sports 3-5 days/week): BMR x 1.55
Very active (hard exercise/sports 6-7 days a week):  BMR x 1.725
Extra active (very hard exercise/sports & physical job or 2x training): BMR x 1.9

Keep in mind that these are estimates in order to help you understand that amount of calories you burn according to your activity level.  If you goal is to lose weight then we recommend doing your best to eat an average of 500 calories less than your BMR and use your activity factor to really accelerate your fat loss.

A Note on Body Fat %

A person’s body fat percentage is actually a bit difficult to determine with precision, and many online calculators use the simplest calculation which also has the greatest room for error in the calculation.  The body composition calculator in this post uses the U.S. Navy body fat formula in order to determine your body fat percentage.  In a study conducted by the U.S. Navy this method was shown to be as accurate as skin fold testing with calipers.  With that said, it should be understood that there is still a margin of error of +/- 2-3%.  Instead of interpreting the body fat percentage given as exact fact, we recommend using it as a starting point with which to track progress.  Be consistent with the method you use to measure your body fat and you will be able to monitor you progress. If you change from one method to another then you will not be able to monitor progress as every method has varying margins of error.

For your reference, below is a table showing the classifications of body fat percentage:

Percentage of  body fat: Body Status
Women Men
10 to 12 2 to 4 Essential fat
14 to 20 6 to 13 Athletes
21 to 24 14 to 17 Fitness
25 to 31 18 to 25 Acceptable
32% or more 26% or more Obese

We hope this post has helped to clarify the difference between BMI and BMR and how they should be used and interpreted.   Once you have your numbers provided by this weight loss calculator then you are empowered with the knowledge of your daily calorie needs and can use this information to begin your weight loss journey.

We wish you the best of luck!

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5 Comments

Leave a comment
  1. Great calculator and a good starting point for weight loss. Body fat readings tend to be all over the place but the Navy method seems somewhat reasonable.

  2. Bryan / Oct 9 2011

    WOW,

    Love the calculator, I have been search the web for an easy to understand system for calculating BMI and this is by far the easist that I have found.

    Bryan

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