Body Mass Index from height and weight. BMI is a population-level screening tool — not a personal health diagnosis. About this calculation ↓
The Body Mass Index formula was devised in 1832 by Belgian statistician Adolphe Quetelet (originally the “Quetelet index”) and renamed by physiologist Ancel Keys in a 1972 paper in the Journal of Chronic Diseases. The default category thresholds shown above (Underweight <18.5, Normal 18.5–25, Overweight 25–30, Obese ≥30) follow the World Health Organization classification for adults.
BMI is endorsed as a population-level screening tool by the WHO, the U.S. Centers for Disease Control, and the National Institutes of Health. In 2023 the American Medical Association adopted a policy noting that BMI is an imperfect measure for individual assessment — it does not distinguish fat from muscle, account for fat distribution, or adjust for sex, ethnicity, or age — and recommended it be used alongside complementary measures such as body-composition analysis or waist-to-hip ratio. The Personalize result panel above lets you apply these adjustments to your own result.
The WHO and the UK's National Institute for Health and Care Excellence (NICE) recommend lower BMI cut-offs for people of South Asian, Chinese, and other Asian descent: overweight at BMI ≥23 and obese at ≥27.5, compared with ≥25 and ≥30 in the standard chart. This is because cardiometabolic risk — type 2 diabetes, cardiovascular disease — rises at a lower BMI in these populations, driven by a higher proportion of visceral fat at the same body weight.
In adults aged 65 and over, a BMI in the 25–27 range is often associated with lower mortality than a strictly “normal” BMI. Maintaining muscle mass and some weight reserve tends to matter more than hitting the under-25 threshold — unintentional weight loss in older adults is a stronger warning signal than being slightly overweight.
Waist circumference measures central (visceral) adiposity, which is a stronger predictor of cardiometabolic risk than BMI alone. Increased risk begins at a waist of 94 cm (37 in) for men and 80 cm (31.5 in) for women; high risk begins at 102 cm (40 in) for men and 88 cm (34.5 in) for women. A person with a “normal” BMI but an elevated waist may still carry meaningful health risk, and a person with an “overweight” BMI but a low waist typically does not.
At the same BMI, women typically carry more body fat than men, and men typically carry more muscle. BMI cannot distinguish the two, which is why a muscular build can push BMI into the overweight range without elevated health risk, and why a sedentary person with a “normal” BMI can still have high body fat percentage (sometimes called “normal-weight obesity”).
Medical disclaimer. This calculator is for general educational use and is not medical advice, diagnosis, or treatment. BMI, target weights, and calorie or activity targets shown here are estimates based on population averages and do not account for medical conditions, medications, pregnancy, history of disordered eating, or individual metabolic differences. Consult a qualified healthcare professional before starting any weight-loss program, changing your diet, or beginning a new exercise regimen — especially if you are under 18, pregnant or breastfeeding, have a chronic condition, or have a history of eating disorders.