BMI Calculator — Check Your Body Mass Index
Calculate your BMI instantly and understand what your score means for your health.
Your BMI
| Category | BMI Range (kg/m²) |
|---|---|
| Underweight | < 18.5 |
| Normal weight | 18.5 – 24.9 |
| Overweight | 25.0 – 29.9 |
| Obesity Class I | 30.0 – 34.9 |
| Obesity Class II | 35.0 – 39.9 |
| Obesity Class III | ≥ 40.0 |
What Is BMI (Body Mass Index)?
Body Mass Index (BMI) is a simple numerical value derived from your weight and height. It is one of the most widely used screening tools to categorize individuals into weight status groups — underweight, normal weight, overweight, and obese. Healthcare professionals around the world rely on BMI as a quick indicator of potential health risks associated with body weight.
The formula for BMI is: BMI = weight (kg) ÷ height² (m²). While BMI does not measure body fat directly, research shows it correlates reasonably well with more direct measures of body fat such as skinfold thickness and dual-energy X-ray absorptiometry (DEXA).
How to Calculate BMI
Using our free online BMI calculator above, simply enter your age, gender, height, and weight. The tool supports both metric (kilograms and centimeters) and imperial (pounds, feet, and inches) units. Your result is displayed instantly along with a color-coded gauge and category classification.
BMI Formula (Metric)
BMI = Weight (kg) ÷ [Height (m)]²
BMI Formula (Imperial)
BMI = [Weight (lbs) ÷ Height (in)²] × 703
BMI Categories Explained
- Underweight (BMI < 18.5): May indicate malnutrition, eating disorders, or other underlying health conditions. Consult a healthcare provider for guidance.
- Normal weight (BMI 18.5–24.9): Generally associated with the lowest health risks. Maintain a balanced diet and regular physical activity.
- Overweight (BMI 25–29.9): Increased risk for cardiovascular disease, type 2 diabetes, and hypertension. Lifestyle modifications are recommended.
- Obesity Class I (BMI 30–34.9): Moderate health risk. Medical evaluation and structured weight management plans are advisable.
- Obesity Class II (BMI 35–39.9): High health risk. Professional medical intervention is strongly recommended.
- Obesity Class III (BMI ≥ 40): Very high health risk, also known as severe or morbid obesity. Comprehensive treatment including medical supervision is essential.
Why Is Knowing Your BMI Important?
Tracking your BMI helps you stay aware of your weight status and its potential impact on your overall health. A BMI outside the normal range can be an early warning sign for conditions such as:
- Heart disease and stroke
- Type 2 diabetes
- High blood pressure (hypertension)
- Certain types of cancer
- Sleep apnea and respiratory problems
- Osteoarthritis and joint issues
Regular BMI checks, combined with other health metrics like waist circumference and blood pressure, give you a more complete picture of your health. Learn more about maintaining a healthy lifestyle on our Fitness & Exercise and Nutrition pages.
Limitations of BMI
While BMI is a useful screening tool, it has some limitations:
- It does not differentiate between muscle mass and fat mass — athletes may have a high BMI but low body fat.
- It does not account for fat distribution. Abdominal fat (visceral fat) carries higher health risks than fat stored in other areas.
- Age, gender, and ethnicity can influence the relationship between BMI and body fat percentage.
- It may not be accurate for pregnant or breastfeeding women, elderly individuals, or growing children.
For a more comprehensive assessment, consider combining BMI with waist-to-hip ratio, body fat percentage measurements, and regular health check-ups. The World Health Organization (WHO) provides detailed guidelines on interpreting BMI across different populations.
Tips to Maintain a Healthy BMI
- Eat a balanced diet: Focus on whole grains, lean proteins, fruits, vegetables, and healthy fats. Explore our Healthy Recipes for meal ideas.
- Stay physically active: Aim for at least 150 minutes of moderate aerobic activity per week. Check out our Yoga section for beginner-friendly routines.
- Get adequate sleep: Poor sleep is linked to weight gain and metabolic disruption.
- Manage stress: Chronic stress can lead to emotional eating and weight gain. Visit our Home Remedies page for natural stress-relief techniques.
- Stay hydrated: Drinking enough water supports metabolism and helps control appetite.
- Consult professionals: Work with a registered dietitian or healthcare provider for personalized advice.
BMI for Children and Teens
For children and adolescents aged 2–19, BMI is interpreted differently. Instead of fixed thresholds, BMI-for-age percentiles are used because body composition varies with age and sex during growth. The CDC's BMI Percentile Calculator for Children is a helpful resource for parents and pediatricians.
Frequently Asked Questions About BMI
A healthy BMI for adults falls between 18.5 and 24.9 kg/m². This range is associated with the lowest risk of weight-related health problems. However, individual health depends on many factors beyond BMI alone.
BMI may overestimate body fat in athletes and people with high muscle mass because it cannot distinguish between muscle and fat. In such cases, body fat percentage or DEXA scans provide more accurate assessments.
It is a good practice to check your BMI every 3 to 6 months, especially if you are actively working on weight management. Regular monitoring helps you track progress and make timely adjustments to your diet and exercise routine.
BMI is a screening tool, not a diagnostic one. A high BMI can indicate increased risk for conditions like heart disease, diabetes, and hypertension, but it should be used alongside other health assessments for a complete picture.
BMI is calculated from height and weight and provides a general weight category. Body fat percentage measures the actual proportion of fat in your body. While BMI is easier to calculate, body fat percentage gives a more precise picture of body composition.
For adults, the same BMI thresholds apply regardless of age and gender. However, women generally have more body fat than men at the same BMI, and older adults tend to have more body fat than younger adults. For children and teens, BMI is interpreted using age- and sex-specific percentiles.