Body Mass Index compares your weight to your height to give a quick, population-level screen for weight status. It's the first number most doctors glance at, not because it's perfect, but because it's fast, free, and correlates reasonably well with health risk across large groups of people.
Ranges: under 18.5 underweight · 18.5–24.9 healthy · 25–29.9 overweight · 30+ obese.
Use BMI as a quick first check-in on your weight relative to your height, or to track how that ratio shifts over months or years. It's most useful for general population screening and long-term trend-watching, not as a precise verdict on any one person's health. If you're a competitive athlete, bodybuilder, pregnant, elderly, or still growing, treat your result as a loose reference rather than a diagnosis, and lean on body fat percentage or a doctor's assessment instead.
BMI is weight in kilograms divided by height in metres squared. The result sorts into four broad bands: under 18.5 is considered underweight, 18.5 to 24.9 is the healthy range, 25 to 29.9 is overweight, and 30 and above is classed as obese. It's a useful screening number, but it can't tell the difference between muscle and fat, so athletes and very muscular people often score higher than their actual body composition would suggest.
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