Your measurements
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Your BMI result
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—Healthy min (kg)
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—Ideal weight (kg)
For guidance only — not financial, tax or legal advice. Verify with a qualified professional.
BMI — frequently asked questions
How accurate is BMI as a health measure?
BMI is a useful screening tool but it has well-known limitations. It does not distinguish between fat and muscle — an athlete or someone with high muscle mass may have a "overweight" BMI despite being very healthy. It also doesn't account for where fat is distributed on your body (visceral vs subcutaneous fat). That said, at a population level BMI correlates well with health outcomes, which is why the NHS uses it as an initial assessment tool alongside other measures.
What are the NHS BMI categories?
The NHS uses the following BMI ranges for adults: Underweight is below 18.5; Healthy weight is 18.5 to 24.9; Overweight is 25 to 29.9; Obese Class I is 30 to 34.9; Obese Class II is 35 to 39.9; and Obese Class III (sometimes called morbidly obese) is 40 and above. Note that these thresholds may be adjusted slightly for certain ethnic groups — for example, South Asian, Chinese, and Black African-Caribbean adults may be assessed at lower thresholds (e.g. overweight at 23+) due to higher health risks at lower BMI values.
Does BMI account for muscle mass?
No — this is the most common criticism of BMI. Because the formula only uses height and weight, a heavily muscled person such as a rugby player or bodybuilder will often fall into the "overweight" or even "obese" category despite having low body fat. Conversely, someone with a healthy BMI but very little muscle ("skinny fat") may have higher-than-ideal body fat. For a more accurate picture, consider also measuring your waist circumference, body fat percentage, or waist-to-height ratio.
What is a healthy waist circumference as an alternative?
Waist circumference is a useful complement to BMI because it measures abdominal fat, which is more strongly linked to heart disease and type 2 diabetes. According to NHS guidelines, health risks increase significantly if your waist measures more than 94 cm (37 inches) for men or 80 cm (31.5 inches) for women. Risks are very high above 102 cm (40 inches) for men or 88 cm (34.5 inches) for women. The waist-to-height ratio (waist ÷ height, ideally below 0.5) is also considered a strong predictor of metabolic health.
Is BMI different for older adults or children?
For children and young people under 18, BMI is interpreted differently using age- and sex-specific centile charts rather than fixed thresholds. For older adults (65+), the NHS notes that a slightly higher BMI (around 25) may actually be protective. Muscle loss (sarcopenia) with age means the same BMI can represent a higher body fat percentage than in younger adults. If you're over 65, discuss your healthy weight range with your GP, as the standard thresholds may not apply directly.