Hi there and NHS BMI Calculator error

Hi there, I now lost 16 Kg, but I don't think the NHS BMI Calculator takes muscle mass into account. When I measured my muscle mass with 3 professional scales I have got 40% muscle mass. This is way above average, and justified, as I have a very physically demanding job. Muscles are denser as they contain less water than fat, so it matters a great deal when the NHS BMI Calculator only gives me the option to enter "moderate" activity! Does anybody know a more accurate calculator?


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11 Replies

  • I think they are all just a guide, but you could try this one bestbmicalculator.com/calcu...

    It's a lot more detailed.

  • Thanks Caz! This one is much better. It clearly shows, I am only 5 BMI points away from a healthy weight. And in fact I have only 27.4% body fat mass, unlike the result of my Salter scale at home, that tells me it's 35.3% (which is largely due to me having a bit of hyperhydrosis, which makes the measuring current flow easier). When I look at myself in the mirror and in cameras and manually feel my belly fat, I feel in far better condition than I used to be. In fact I look very much like in my last university years, which is quite an achievement, something that my fiancé picked up on as well.

  • Pleased you found it helpful and good to hear you are feeling happy.

  • Thanks Caz! I mean it's so detrimental not accounting for the muscle mass, I am walking around 17 miles each week (measured accurately through Google Fit and not accounting for time walked inside home or store) plus I am working physically really hard. The Monday before last I worked 10 hours straight and the Sunday before 7 hours!

  • Also the faulty NHS BMI Calculator rounds up from a BMI of 30.03 to 30.1, whereas in fact it should tell me I am not obese, but rather overweight.

  • Hi and welcome, jazzjohannes :)

    See if this suits you better


    Take a look at the Pinned posts section to the right of your screen (bottom if you're using a mobile), or in the drop down on the 'Posts' page (it says 'arrange by'). Read the Welcome Newbie thread, then move through to the challenges, where we hope you'll find at least one that will appeal to you.

    Move down to the Topics, to find a variety of threads, collated into specific topics for ease of access and we ask that you also 'file' your own threads, so that others won't miss your important news.

    Take a look at the NHS 12 week plan, as a lot of people have been successful with it. Don't forget to take your starting measurements and a 'before' picture, as they can be very motivating on days that the scales refuse to co-operate.

    We run a weigh-in every day of the week and you'd be very welcome to join one of them. The threads can always be found in the Events section, to the right of the HOME page, bottom on a mobile.

    We also run a Daily Diary, where we share our meal and exercise plans for the day. It's a great place to get ideas and to keep us focused. The link can also be found in Events.

    Be aware, that the HU app doesn't give you access to all of our important features, so we advise that you use the full website page.

    We've found that to get the best out of this community, we need to be active on the forum, as it's where we exchange information, get motivation and inspiration and make friends. We hope that you'll join us here, regularly, too.

    It's only left for me to wish you well on your journey :)

  • BMI is a very blunt tool when it comes to any outliers. When I was at my leanest/strongest, my body fat was down around 5 to 7 percent yet the BMI calculator had me on the borderline between overweight and obese. Calculating using only weight and height is only ever going to work for people in the middle of the bell curve heightwise for starters. Tall people will be classed as fatter and short people thinner and it will have nothing to do with the amount of adipose tissue they are carrying.

    A couple of famous examples of this are Brad Pitt, who, at the time of Fight Club, would have been classed as 'Very Overweight' and rugby star Johnny Wilkinson who in his England prime ranked as 'Obese'.

    Similarly, if you are 5' 0" you can be carrying around 43 percent body fat and still be on the underweight end of 'Ideal'.

    I would also be very sceptical about the body fat/lean mass readings on scales. They simply are not accurate. The only reliable ways of measuring body fat are using calipers or the pro methods like dexa scan or underwater weighing.

  • A BMI of weight/height^3 would be less 'heightist' than the current weight/height^2.

  • There is no physiological reason to square the height in the first place. It was simply a shortcut taken by the mathematician (note: not doctor) who devised the formula to make it fit the data he had.

    Of course the other point that this raises is that all of the statistics we are constantly bombarded with regarding what percentage of the population is overweight or obese, are based on BMI.

    Also life insurance and health insurance premiums are calculated on BMI. Not that I am being cynical or conspiracist or anything. I am sure the insurance companies would not dream of levying higher premiums from people who are actually tall, lean and muscled based on a bogus principle.

    (cont. p.294...)

  • Actually, muscles are more dense than fat because they contain more water, not less.

    Provided you don't suffer body image distortion, the mirror is a good guide.

  • Oh thanks for the info, I just assumed before checking those details in particular. So in a way actually, fat must be just a 'very visible' expansion of webbed material then! Another reason not to give into shaming yourself or others and rather see them for who they really are!

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