BMI Calculator
Calculate your Body Mass Index (BMI) to assess if you're at a healthy weight. Get instant results with health recommendations, ideal weight range, and understand what your BMI means for your health.
What is BMI (Body Mass Index)?
Body Mass Index (BMI) is a simple calculation using a person's height and weight. The BMI formula was invented by Adolphe Quetelet in the 1830s. It is used to categorize individuals into different weight categories: underweight, normal weight, overweight, and obese. While BMI is a useful screening tool, it's not a diagnostic measure of body fatness or health.
How is BMI Calculated?
BMI = weight (kg) / height² (m²)
BMI = (weight (lbs) / height² (in²)) × 703
BMI Categories (Adults)
| Category | BMI Range | Health Risk |
|---|---|---|
| Underweight | Less than 18.5 | Malnutrition, bone loss, decreased immunity |
| Normal weight | 18.5 - 24.9 | Low risk (healthy range) |
| Overweight | 25.0 - 29.9 | Moderate risk of health issues |
| Obesity Class I | 30.0 - 34.9 | High risk of health issues |
| Obesity Class II | 35.0 - 39.9 | Very high risk of health issues |
| Obesity Class III | 40.0 or greater | Extremely high risk of health issues |
Understanding Your BMI
- Underweight (BMI < 18.5): May indicate malnutrition, eating disorders, or other health problems. Consult a healthcare provider.
- Normal weight (BMI 18.5-24.9): Associated with the lowest risk of weight-related health problems. Maintain through balanced diet and exercise.
- Overweight (BMI 25-29.9): Slightly elevated risk for heart disease, diabetes, and other conditions. Lifestyle changes recommended.
- Obese (BMI ≥ 30): Higher risk for serious health conditions including heart disease, diabetes, stroke, and certain cancers. Medical consultation advised.
Limitations of BMI
While BMI is a useful screening tool, it has several limitations:
- Doesn't measure body fat directly: Athletes with high muscle mass may have high BMI but low body fat
- Doesn't account for muscle vs. fat: Two people with same BMI can have very different body compositions
- Age differences: Older adults naturally have more body fat than younger adults at the same BMI
- Gender differences: Women naturally have more body fat than men at the same BMI
- Ethnicity variations: Health risks occur at different BMI levels for different ethnic groups
- Frame size not considered: People with larger frames may naturally weigh more
- Pregnancy: BMI is not accurate during pregnancy
Beyond BMI: Other Health Indicators
Measures abdominal fat. Health risks increase with waist over 40" (men) or 35" (women).
More accurate than BMI. Healthy range: 10-20% (men), 18-28% (women).
Compares waist to hip measurement. Indicates fat distribution pattern.
Tips for Achieving a Healthy Weight
- Balanced diet: Focus on whole foods, fruits, vegetables, lean proteins, and whole grains
- Portion control: Be mindful of serving sizes to avoid overeating
- Regular exercise: Aim for 150 minutes of moderate activity per week
- Stay hydrated: Drink plenty of water throughout the day
- Sleep well: 7-9 hours of quality sleep supports healthy weight
- Manage stress: Chronic stress can lead to weight gain
- Avoid crash diets: Sustainable lifestyle changes work better than quick fixes
- Seek support: Consult healthcare providers, nutritionists, or support groups
- Track progress: Monitor weight and measurements, but don't obsess over numbers
- Be patient: Healthy weight loss is 1-2 pounds per week
Frequently Asked Questions
What is a healthy BMI?
For most adults, a healthy BMI is between 18.5 and 24.9. This range is associated with the lowest risk of weight-related health problems. However, individual health varies, so consult with a healthcare provider for personalized advice.
Is BMI accurate for athletes?
No, BMI can be misleading for athletes and bodybuilders. Since muscle weighs more than fat, very fit individuals may have a high BMI despite having low body fat. In these cases, body fat percentage is a better indicator.
Does BMI differ for men and women?
The BMI calculation is the same for both men and women, but women naturally have more body fat than men at the same BMI. Health professionals consider this when interpreting BMI results.
Can I use BMI for children?
BMI for children and teens (ages 2-19) is calculated the same way but interpreted differently using age and sex-specific percentile charts. This calculator is designed for adults 20 and older.
How often should I check my BMI?
For most people, checking BMI once a month is sufficient when working toward weight goals. Weekly measurements can show natural fluctuations that aren't meaningful. Focus on long-term trends rather than daily changes.
Is my data stored or shared?
No, all calculations happen entirely in your browser using JavaScript. Your personal health information never leaves your device and is not stored or transmitted anywhere.