Health Calculators
BMI Calculator
Calculate your Body Mass Index (BMI) based on your height and weight. BMI is a widely used screening tool that estimates body fat and helps identify potential health risks.
Formula Used
BMI = Weight (kg) Γ· [Height (m)]Β²
About This Calculator
What It Does
Calculate your Body Mass Index from your height and weight. BMI is a widely-used screening tool that estimates body fat and categorizes results as underweight, normal weight, overweight, or obese using standard WHO thresholds. While useful for population-level health trends, BMI does not distinguish between muscle and fat mass, so athletes or muscular individuals may show a high BMI despite low body fat. It does not account for age, sex, bone density, or fat distribution either. Use BMI as a starting point for health awareness, not as a standalone medical diagnosis. For a complete picture, pair it with waist circumference, body fat percentage, and blood work.
Worked Example
Example 1 β Normal weight: A person weighing 70 kg at 170 cm. Height in meters = 1.70 m. BMI = 70 Γ· (1.70 Γ 1.70) = 70 Γ· 2.89 β 24.2. This is in the 'Normal weight' category (18.5β24.9). Example 2 β Overweight: A person weighing 85 kg at 170 cm. BMI = 85 Γ· 2.89 β 29.4. This is just under the obese threshold (30), falling in the 'Overweight' category (25β29.9). At this level, doctors may recommend lifestyle changes to prevent progression to obesity. Example 3 β Obese: A person weighing 105 kg at 170 cm. BMI = 105 Γ· 2.89 β 36.3. This is in the 'Obese Class II' category (35β39.9). At this level, medical consultation is recommended to discuss weight management strategies including diet, exercise, and potential medical interventions. Edge case β Athlete: A rugby player weighing 95 kg at 180 cm. BMI = 95 Γ· (1.80 Γ 1.80) = 95 Γ· 3.24 β 29.3 ('Overweight'). Despite a healthy body fat percentage, BMI flags them as overweight. This is the classic limitation of BMI: it cannot distinguish muscle from fat.
Real-World Usage
Use BMI for general health screening at annual checkups β most doctors calculate it as part of a routine physical. Track changes over time: a BMI trending upward may signal gradual weight gain before it becomes a health concern. Fitness professionals use BMI as one of several metrics alongside body fat calipers and bioelectrical impedance. Life insurance companies often reference BMI ranges when setting premiums. Public health organizations use population BMI data to track obesity trends and allocate resources. For pregnant women, different BMI charts apply β standard BMI thresholds do not account for gestational weight gain. Athletes should interpret BMI cautiously and prefer body composition testing.
Local Context
WHO thresholds apply worldwide: below 18.5 is underweight, 18.5β24.9 is normal, 25β29.9 is overweight, and 30+ is obese. In the United States, about 42% of adults are obese (BMI 30+), making it one of the highest rates globally. The NHS in the UK uses the same thresholds but combines BMI with waist-to-height ratio for a more accurate assessment starting in 2025. Canada's clinical guidelines additionally recommend measuring waist circumference for anyone with a BMI over 25. While BMI is standardized globally, some Asian countries (Japan, South Korea, China) have adopted lower overweight thresholds (BMI 23+) because research shows higher metabolic risk at lower BMIs in these populations.
Sources and Methodology
BMI is calculated as weight divided by height squared and interpreted using standard adult BMI categories. The method follows public-health references such as the World Health Organization and CDC BMI guidance. BMI is a screening measure only and does not diagnose health status or body composition.
Last reviewed: May 2026.
Frequently Asked Questions
What BMI ranges indicate a healthy weight?
According to the WHO: below 18.5 is underweight, 18.5β24.9 is normal weight, 25β29.9 is overweight, and 30+ is obese.
Is BMI accurate for everyone?
BMI does not distinguish between muscle and fat, so very muscular individuals may be classified as overweight or obese despite having low body fat. It is one screening tool β not a diagnosis.
Should children use this BMI calculator?
No. This calculator is designed for adults aged 20 and over. Children and teens should use age- and sex-specific BMI percentiles, as their bodies are still developing.