Body fat maths

I am using a fat monitor as well as scales, at the end of the day, its body fat I want to reduce so it seems to make sense to measure that.

One of the calcs I find useful is to work out a realistic target weight. This also acts a useful cross check that my weight has not been thrown out by being dehyrated.


Total weight * body fat percentage = weight of fat.

Total weight – weight of fat = theoretical fat free weight (this should remain fairly constant unless you are gaining significant muscle mass)

Target weight = fat free weight + target weight * target body fat percentage.

ie Target weight = fat free weight/(1 – target body fat percentage)

With my numbers from yesterday:

88kg * 30% = 26.4 kg of fat

Fat free weight = 88 – 26.4 = 61.6 kg

Target weight = 61.6/(1 – 0. 15) = 72.5 kg

That means I’ve got 15.5kg (34 lbs) of fat to lose – most of my kids weight less than that!

I actually think this is wrong and I may need to lose more, as time goes on and I get more weight/fat readings I’ll be able to fine tune it. 15.5 is near enough for now.

(where did the 0.15 target body fat come from? I googled ‘ideal body fat percentage’)(and my fat monitor came with a guide)

What are your stats?


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