BMI Calculator
Check your Body Mass Index and see where you stand
Understanding Your BMI Result
Body Mass Index (BMI) is the quickest way to check whether your weight is in the healthy range for your height. Developed by Belgian statistician Adolphe Quetelet in the 1830s and adopted as a public health screening tool by the WHO in 1985, BMI remains the most widely-used weight classification method worldwide — though it's not without limitations.
BMI is calculated as weight in kilograms divided by height in meters squared (kg/m²). The WHO classifies a BMI below 18.5 as underweight, 18.5–24.9 as normal, 25–29.9 as overweight, and 30 or higher as obese. These categories correlate with statistical risk for cardiovascular disease, type 2 diabetes, and certain cancers — but correlation isn't destiny, and individual health varies widely.
The biggest limitation of BMI is that it treats all body mass the same. A bodybuilder with 8% body fat and a sedentary office worker with 30% body fat can have identical BMIs because BMI can't distinguish muscle from fat. This is why athletes frequently register as 'overweight' or 'obese' despite being extremely lean. BMI also doesn't account for bone density, fluid retention, or fat distribution — abdominal fat (visceral) carries more health risk than fat stored in hips or thighs.
For most adults aged 20-65 with average activity levels, BMI provides a reasonable first screen. If you're athletic, pregnant, postpartum, elderly, of Asian descent (where health risks start at BMI 23 rather than 25), or recovering from illness, pair BMI with other metrics: waist-to-hip ratio, body fat percentage, or a DEXA scan. A qualified healthcare provider can interpret your BMI in the context of your full health picture.
Keep learning
- →BMI Explained: What Your Number Really MeansDeep-dive into BMI interpretation, limitations, and alternatives.
- →How to Lose Belly Fat (Science-Based)Visceral fat is what BMI misses. Here's how to target it.
- →How Much Protein Do You Need?Preserve muscle while losing weight — the protein math.
- →Maintenance Calorie CalculatorOnce you know your BMI, calculate the calories to reach goal weight.
BMI Calculator FAQ
BMI (Body Mass Index) is a simple screening metric calculated by dividing your weight in kilograms by your height in meters squared (kg/m²). It provides a rough estimate of body fatness based on height and weight alone.
BMI does not distinguish between muscle and fat mass. Athletes, bodybuilders, and people with above-average muscle mass often show an 'overweight' BMI despite being healthy and lean. In these cases, body fat percentage or waist circumference are better indicators.
The WHO classifies a BMI between 18.5 and 24.9 as 'normal weight.' Below 18.5 is considered underweight, 25-29.9 is overweight, and 30+ is classified as obese. However, these ranges are population-level guidelines — individual health depends on many factors beyond BMI.
For general health monitoring, checking BMI once a month is sufficient. If you are actively losing or gaining weight, weekly checks can help track trends. Remember that daily fluctuations in water weight are normal and do not reflect real changes in body composition.
The standard BMI formula does not adjust for age or gender, though body composition changes with both. Older adults naturally lose muscle mass, meaning the same BMI may represent more body fat. Some health organizations use adjusted thresholds for elderly populations.