Formulas - Target Body Weight

Okay, You now know how to calculate your BMI now lets use that to calculate your target body weight. You will need to know three pieces of information for this formula: (your current weight, your body fat content; for this example we will use BMI as well as a more accurate skin fold measurement, and the body fat percentage you wish to be at).

Lets use me as an example again:

I weigh 160
My body fat content is 26 according to BMI
Optional: My body fat content by skin fold analysis is 15.2 (a much more accurate number)
I would like to be at a body fat content of 14% to 17% (fitness level)

Lets go back to the table I listed in my last post(http://personal-trainer-nj.blogspot.com/2008/06/next-post-theme-formulas.html)

Classification*** Woman (% fat)*** Men (% fat)
Essential fat****10 - 13%*********2 - 5%
Athletes*******14 - 20%*********6 - 13%
Fitness********21 - 24%*********14 - 17%
Average*******25 - 31%*********18 - 24%
Obese*********32% or higher****25% or higher

Here is the formula:
Fat mass = current body weight * (%body fat / 100%)
Fat-free mass = current body weight - fat mass
Target body weight = fat-free mass / 1 - (goal body fat percentage / 100)

Lets plug the numbers for my specs (we will use the BMI results first):
Fat mass = 160 * (26 /100) or 160 * 0.26 or 41.6 pounds.
Fat-free mass = 160 - 41.6 or 118.4 pounds.
Target body weight = 118.4 / 1 - (14% / 100) or 118.4 / 1 - 0.14 or 118.4 / 0.86 or 138 pounds for the low end of my goal.
Target body weight = 118.4 / 1 - (17% / 100) or 118.4 / 1 - 0.17 or 118.4 / 0.83 or 143 pounds for the high end of my goal.

So if I utilized BMI for my body fat percentage I need to get my weight of 160 pounds down to a weight range of 138 - 143 pounds.

But lets see what that weight becomes if I I utilize a more accurate body fat number (skin fold measurements). What do you think will happen? Take a guess and see if you are right.

Fat mass = 160 * (15.2 / 100) or 160 * .152 or 24.32 pounds.
Fat-free mass = 160 - 24.32 or 135.68 pounds.
Target body weight = 135.68 / 1 - (14% / 100) or 135.68 / 1 - (0.14) or 135.68 / 0.86 or 158 pounds for the low end of my goal.
Target body weight = 135.68 / 1 - (17% / 100) or 135.68 / 1 - (0.17) or 135.68 / 0.83 or 163 pounds for the high end of my goal.

So by using a more accurate measurement I clearly see I am at ideal weight. If you fit the profile that I outlined in post http://personal-trainer-nj.blogspot.com/2008/06/next-post-theme-formulas.html for BMI calculation then you can use this formula and get a pretty accurate picture of what you should weigh based on your goal body fat percentage. If not then you need to utilize either a skin-fold measurement assessment(most gyms offer this free to their members) or utilize one of the scales out on the market that can give you a better picture (deviation of about +/-5%) of what your body fat percentage is.

This is a great formula that I utilize daily for my clients goals. And you should use it as well. It gives you a goal to reach for. Knowing exactly what you should weigh is a primary goal for anyone looking to lose weight. If you have any questions or confusion about the formulas let me know and I will walk you through it.

As always - I am available for personal training either in person (if in NJ) or over the web. My rates are $75.00 per hour for in-person training and $25.00 per hour for email personal training. If you feel you have stalled in your pursuit of fitness and need some expert knowledge to get you on track reach out to me.

Regards,

Eddie Camaroto CPT