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Everyday & Life · NHS thresholds

NHS BMI Calculator

Body Mass Index is the NHS’ quick screening for whether you’re a healthy weight for your height. It’s imperfect — it doesn’t distinguish muscle from fat — but it’s a useful first signal.

cm
kg

Your BMI

24.5

Healthy weight

Underweight: < 18.5
Healthy: 18.5 – 25
Overweight: 25 – 30
Obese: ≥ 30

How we calculated your result

BMI = weight (kg) ÷ height² (m²). NHS thresholds for adults: 18.5 / 25 / 30. For higher-risk backgrounds, the overweight threshold drops to 23 and obese to 27.5.

Official UK rules in simple English

  • Standard: under 18.5 underweight; 18.5–24.9 healthy; 25–29.9 overweight; 30+ obese.
  • NICE NG7 recommends lower thresholds (23 / 27.5) for South Asian, Chinese, Black African, Caribbean and Middle Eastern adults.
  • Children, pregnant women, athletes — BMI isn’t valid.

Common pitfalls to watch out for

  • ⚠ Muscular? BMI is misleading

    Rugby players, bodybuilders, regular gym-goers can hit ‘obese’ while being healthy. Combine with waist-to-height ratio for a better picture.

  • ⚠ Doesn’t track location of fat

    Central (belly) fat is metabolically worse than peripheral. Waist circumference matters too — under 94cm (men) / 80cm (women) is the NHS guideline.

  • ⚠ Not for under-18s

    Children use BMI-for-age percentiles. Talk to your GP.

Frequently asked questions

Why the lower threshold for some backgrounds?
Research (NICE NG7) shows people of South Asian, Black African and similar heritage develop type 2 diabetes and heart disease at lower BMIs than white Europeans.
What's a healthy waist size?
Under half your height. Quick test: piece of string folded to your height — should reach around your waist with slack.

Screening tool, not a diagnosis. Talk to your GP for personal advice.

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