BMI is one number.
Here's what it actually means.
Body Mass Index is the most quoted health metric in the world — and the most misunderstood. We'll calculate yours, plot it on the scale, and tell you exactly what it does and doesn't say about your body.
Your BMI of 24.2 sits comfortably in the healthy weight range. Your goal here is maintenance — keeping the body composition you have while improving energy, sleep and how food fits into your life. Body recomposition (gaining muscle, losing fat at the same weight) is the most realistic next step.
How we got to your number.
No black box. The same equation used by the NHS, the WHO and every clinician you've ever seen. Here's the calculation laid out so you can follow it yourself.
Apply the BMI formula
BMI is your weight relative to the square of your height. The original equation was derived in 1832 by Belgian statistician Adolphe Quetelet — the formula is unchanged nearly two centuries later.
The unit is kg/m² — although nobody uses it in conversation. The squared-height term is what makes BMI a population-level proxy for body composition: it normalises weight against the fact that taller people are also wider and deeper, not just taller.
Match to a category
Once we have the number, we match it against the standard cut-offs used by the World Health Organisation and adopted by the NHS.
These thresholds are based on large-scale epidemiological data correlating BMI with all-cause mortality. They are the same in every country that uses WHO classifications, although ethnicity-specific variants exist for South Asian and East Asian populations, where lower thresholds (overweight at 23, obesity at 27.5) better predict metabolic risk.
Calculate your healthy weight range
Your BMI is one number, but the healthy range is a band. Working the formula in reverse tells us what weight you'd need to land at either end of the healthy zone.
We also surface a "target BMI 22" weight. Twenty-two sits right in the middle of the healthy range and is the value most consistently associated with the lowest mortality risk in long-running observational studies. It's the number our app uses internally as the default goal weight when one isn't otherwise specified.
BMI changes as your weight changes — but height stays constant. So the same target weight band applies to you for life. It's the only health metric that's truly fixed.
Where BMI gets it wrong.
BMI is a fast, free, population-level screening tool. It was never designed to assess an individual's health, and it has well-documented blind spots. If you're in any of the situations below, treat your BMI as informational rather than diagnostic.
It can't tell muscle from fat
BMI only sees mass relative to height. A bodybuilder and someone with the same dimensions but no muscle would score identically. If you train heavy and consistently, your BMI will read higher than your body fat percentage warrants.
It treats men and women the same
Women naturally carry more essential body fat than men — usually 6–11% more. The same BMI on a woman and a man represents different body compositions, but the cut-offs don't reflect that.
It ignores where fat sits
Visceral fat (around the organs) is far more metabolically dangerous than subcutaneous fat (under the skin). Two people with the same BMI can have very different cardiovascular risk profiles depending on where they hold weight.
It loses accuracy at the extremes
For very tall, very short, elderly, pregnant, or growing teenage bodies, BMI breaks down. The formula was calibrated on average European adults in the 1800s and was never re-validated for these populations.
For a fuller picture, BMI is best paired with waist circumference, body fat percentage, and how you actually feel — your energy, your sleep, your strength. A number is a starting point. Your body is the rest of the story.
A note on accuracy
The BMI categories shown follow World Health Organisation and NHS classifications for adults aged 18 and over of European descent. Different cut-offs apply for South and East Asian populations and for children. BMI is a screening tool only — it does not diagnose health conditions. If you have concerns about your weight, body composition or metabolic health, please consult a registered dietitian or your GP. This calculator is for informational purposes and is not medical advice.
BMI tells you where.
We tell you what to do next.
Knowing your BMI is the first step. My Nutri AI uses it alongside your goals to build a calorie target, macro split and a full week of meals tailored to your body — recalibrated every Sunday.
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