formula for calculating goal BF% and goal weight

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myofibril
myofibril Posts: 4,500 Member
in Fitness and Exercise
The following method can be used to determine goal body fat percentage (GBF%) in conjunction with goal weight (GW) if this kind of thing is important to you:

1. Multiply total body weight in lbs (TBW) by current body fat percentage (BF%) to determine fat (F).
2. Subtract F from TBW
3. The remaining weight is lean body mass (LBM) otherwise known as fat free mass
4. Set desired GBF%
5. Divide LBM by (1-0.GBF)
6. The answer will be the GW at the desired GBF%
7. Subtract GW from the TBW to determine the amount of scale weight loss (WL) required to achieve GBF%

Worked Example:

200 lb Male currently with a body fat percentage of 20% but wishing to diet down to a body fat of 10% whilst preserving LBM:

Step 1: 200 x 20% = 40
Step 2: 200 - 40 = 160
Step 3: 160
Step 4: 10%
Step 5: 160 / (1-0.10)
Step 6: 177.7 approx
Step 7: 200 - 177.7 = 22.3

So, for our intrepid trainee to get down to 10% body fat they will need to lose about 22lbs of fat and will achieve a target weight of 177 of thereabouts.

Personally, I don't think things like BF% or scale weight at worth worrying about. I don't really care (...much ;) what my weight or body fat % is as long as I look and feel good in myself, I am strong, healthy and fit. Good luck to you whatever your goals may be.

Replies

  • tmontgomery69
    tmontgomery69 Posts: 180
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    Bump
  • GinNouveau
    GinNouveau Posts: 143 Member
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    Awesome info. Thanks!
  • myboysmomx2
    myboysmomx2 Posts: 505 Member
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    Bump! Thanks! :smile:
  • erickirb
    erickirb Posts: 12,293 Member
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    The following method can be used to determine goal body fat percentage (GBF%) in conjunction with goal weight (GW) if this kind of thing is important to you:

    1. Multiply total body weight in lbs (TBW) by current body fat percentage (BF%) to determine fat (F).
    2. Subtract F from TBW
    3. The remaining weight is lean body mass (LBM) otherwise known as fat free mass
    4. Set desired GBF%
    5. Divide LBM by (1-0.GBF)
    6. The answer will be the GW at the desired GBF%
    7. Subtract GW from the TBW to determine the amount of scale weight loss (WL) required to achieve GBF%

    Worked Example:

    200 lb Male currently with a body fat percentage of 20% but wishing to diet down to a body fat of 10% whilst preserving LBM:

    Step 1: 200 x 20% = 40
    Step 2: 200 - 40 = 160
    Step 3: 160
    Step 4: 10%
    Step 5: 160 / (1-0.10)
    Step 6: 177.7 approx
    Step 7: 200 - 177.7 = 22.3

    So, for our intrepid trainee to get down to 10% body fat they will need to lose about 22lbs of fat and will achieve a target weight of 177 of thereabouts.

    Personally, I don't think things like BF% or scale weight at worth worrying about. I don't really care (...much ;) what my weight or body fat % is as long as I look and feel good in myself, I am strong, healthy and fit. Good luck to you whatever your goals may be.

    The problem with this is that while you lose fat you will also lose LBM, so this calculation would not work and your BF% would be higher at that weight. It is best to figure out your goal BF% and just work towards that and measure periodically and ignore the scale. This calc said you would have to lose 22 lbs of fat, but if you lost lean body mass, which you will, you would have to lose more fat than 22 lbs to reach 10% BF, but your total weight will also be lower than the calc shows.

    Most likely in this example the exerciser would have to get down to 165-170ish to achieve the goal BF% due to loss of LBM
  • getsveltEagain
    getsveltEagain Posts: 1,063 Member
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    bump
  • ninerbuff
    ninerbuff Posts: 48,707 Member
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    I'll link with you:

    http://www.myfitnesspal.com/topics/show/304029-a-quick-way-to-figure-out-your-ideal-weight?hl=an+easy+way+to+figure+out+your+goal+weight


    A.C.E. Certified Personal Trainer
    IDEA Fitness member
    Kickboxing Certified Instructor
    Been in fitness for 28+ years and have studied kinesiology and nutrition
  • ninerbuff
    ninerbuff Posts: 48,707 Member
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    The problem with this is that while you lose fat you will also lose LBM, so this calculation would not work and your BF% would be higher at that weight. It is best to figure out your goal BF% and just work towards that and measure periodically and ignore the scale. This calc said you would have to lose 22 lbs of fat, but if you lost lean body mass, which you will, you would have to lose more fat than 22 lbs to reach 10% BF, but your total weight will also be lower than the calc shows.

    Most likely in this example the exerciser would have to get down to 165-170ish to achieve the goal BF% due to loss of LBM
    True that you will lose LBM, but I think that it's a good way to try to target a reasonable weight for an individual compared to BMI. You could always reassess once you're closer to goal.


    A.C.E. Certified Personal Trainer
    IDEA Fitness member
    Kickboxing Certified Instructor
    Been in fitness for 28+ years and have studied kinesiology and nutrition
  • myofibril
    myofibril Posts: 4,500 Member
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    The problem with this is that while you lose fat you will also lose LBM, so this calculation would not work and your BF% would be higher at that weight.

    Yep.

    You can never be 100% accurate because as you say it is probable that you will lose LBM as well as fat when dieting down for most trainees. It will always generate guideline figures never exact totals. The problem with tracking metrics like BF% alone however is that it highly prone to errors in measurement, particularly user error.

    I think if you are going to track in my view it should either scale weight and BF% in conjunction or leave them both alone and go for something more meaningful in my opinion like measurements of fitness (V02 max, 1RM etc.)
  • myofibril
    myofibril Posts: 4,500 Member
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    I'll link with you:

    http://www.myfitnesspal.com/topics/show/304029-a-quick-way-to-figure-out-your-ideal-weight?hl=an+easy+way+to+figure+out+your+goal+weight


    A.C.E. Certified Personal Trainer
    IDEA Fitness member
    Kickboxing Certified Instructor
    Been in fitness for 28+ years and have studied kinesiology and nutrition

    lol - you could have told me that before I wrote that long assed post...
  • lemonadem
    lemonadem Posts: 398 Member
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    Bump
  • Rae6503
    Rae6503 Posts: 6,294 Member
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    Since niner did it.

    http://www.myfitnesspal.com/blog/Rae6503/view/calculate-your-goal-weight-based-on-goal-body-fat-percentage-170958

    ;-)
  • ninerbuff
    ninerbuff Posts: 48,707 Member
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    lol - you could have told me that before I wrote that long assed post...
    It's good for your brain! Plus it's also good to hear other posts from people "in the know" for validation.

    A.C.E. Certified Personal Trainer
    IDEA Fitness member
    Kickboxing Certified Instructor
    Been in fitness for 28+ years and have studied kinesiology and nutrition
  • mamitosami
    mamitosami Posts: 531 Member
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    Bumping to read later... Math--makes my head all crazy-like!:explode:
  • mamitosami
    mamitosami Posts: 531 Member
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    FINALLY did it, with the help of both threads (couldn't figure out the 1-.GBF, duh!). I got 152.5. This was expected. Cool, so great to know this. This last ten pounds is the hardest darn 10 pounds anyone's ever tried to rid themselves of!!! 7 months hard!

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