BMI CALCULATOR
Calculate your Body Mass Index instantly with personalized diet and exercise recommendations. Free, private, and scientifically accurate.
Calculate Your BMI
Personalized Health Recommendations
What is BMI and Why Calculate It?
Body Mass Index (BMI) is a widely-used health screening tool that measures your body fat based on height and weight. Originally developed by Belgian mathematician Adolphe Quetelet in the 1830s, BMI provides a quick assessment of whether your weight falls within a healthy range for your height.
Our BMI calculator is completely free and provides instant results for adults and children. Whether you're monitoring your fitness journey, consulting with healthcare professionals, or simply curious about your health status, this tool offers valuable insights into your overall wellness.
BMI Categories and Weight Classifications
Adult BMI Chart (Ages 20+)
The World Health Organization (WHO) established these BMI ranges for adults aged 20 and older, applicable to both men and women:
| Weight Status | BMI Range (kg/m²) | Health Risk Level |
|---|---|---|
| Severe Thinness | < 16 | High Risk |
| Moderate Thinness | 16 - 17 | Moderate Risk |
| Mild Thinness | 17 - 18.5 | Low Risk |
| Normal Weight | 18.5 - 25 | Lowest Risk |
| Overweight | 25 - 30 | Low to Moderate Risk |
| Obese Class I | 30 - 35 | Moderate Risk |
| Obese Class II | 35 - 40 | High Risk |
| Obese Class III | > 40 | Very High Risk |
Children and Teen BMI (Ages 2-20)
For children and adolescents, BMI is interpreted differently using percentiles that account for age and gender. The CDC provides these guidelines:
- Underweight: Below 5th percentile
- Healthy Weight: 5th to 85th percentile
- At Risk of Overweight: 85th to 95th percentile
- Overweight: Above 95th percentile
Health Implications of BMI Results
Risks of Being Overweight (BMI > 25)
Maintaining a BMI above the normal range can significantly impact your health. Research consistently shows increased risks for:
Cardiovascular Health
- High blood pressure (hypertension)
- Elevated LDL ("bad") cholesterol
- Reduced HDL ("good") cholesterol
- Coronary heart disease
- Stroke
Metabolic Disorders
- Type 2 diabetes
- High triglycerides
- Metabolic syndrome
- Insulin resistance
Other Health Conditions
- Sleep apnea and breathing disorders
- Osteoarthritis (joint disease)
- Gallbladder disease
- Certain cancers (endometrial, breast, colon, kidney, liver)
- Mental health issues including depression and anxiety
Risks of Being Underweight (BMI < 18.5)
While often overlooked, being underweight also poses significant health risks:
- Nutritional Deficiencies: Malnutrition, vitamin deficiencies, and anemia
- Bone Health: Osteoporosis and increased fracture risk
- Immune System: Weakened immunity and increased infection risk
- Reproductive Health: Hormonal imbalances and menstrual irregularities
- Growth Issues: Particularly concerning for children and teens
- Surgical Complications: Higher risks during medical procedures
How to Calculate BMI: Formulas and Examples
Metric System (kg/m²)
The standard BMI formula uses kilograms and meters:
BMI = weight (kg) ÷ height² (m²)
Example: 70 kg ÷ (1.75 m)² = 70 ÷ 3.06 = 22.9 BMI
Imperial System (lbs/in²)
For pounds and inches, multiply by 703:
BMI = (weight in lbs ÷ height² in inches) × 703
Example: (154 lbs ÷ 69² inches) × 703 = 22.7 BMI
Beyond Basic BMI: Advanced Body Composition Metrics
BMI Prime
BMI Prime provides a more intuitive understanding by expressing your BMI as a ratio to the upper healthy limit (25). A BMI Prime of 1.0 means you're at the upper limit of normal weight, while 1.2 indicates 20% above the healthy threshold.
Ponderal Index
The Ponderal Index addresses some BMI limitations for very tall or short individuals by using height cubed instead of squared. This provides more accurate assessments for people at height extremes.
Understanding BMI Limitations
While BMI is an excellent screening tool, it's important to understand its limitations:
Body Composition Factors
- Muscle Mass: Athletes and bodybuilders may have high BMI due to muscle density
- Age Differences: Older adults typically have more body fat at the same BMI
- Gender Variations: Women generally have higher body fat percentages than men at equivalent BMI
- Ethnic Considerations: Different populations may have varying body compositions
When to Consult Healthcare Professionals
BMI should be one part of a comprehensive health assessment. Consider professional consultation when:
- Your BMI falls outside the normal range
- You have concerns about your weight or health
- You're planning significant lifestyle changes
- You have existing health conditions
Taking Action Based on Your BMI Results
For Healthy BMI Maintenance (18.5-25)
- Continue balanced nutrition with whole foods
- Maintain regular physical activity (150+ minutes weekly)
- Monitor weight quarterly
- Focus on overall wellness, not just weight
For Weight Management
- Set realistic, gradual goals (1-2 lbs per week)
- Combine dietary changes with increased activity
- Track progress with multiple metrics, not just BMI
- Consider professional guidance for sustainable results
Frequently Asked Questions About BMI
How often should I calculate my BMI?
For general health monitoring, calculating BMI monthly or quarterly is sufficient. If you're actively trying to change your weight, weekly measurements can help track progress.
Is BMI accurate for all body types?
BMI is accurate for about 90-95% of the population but may not reflect true health status for very muscular individuals, elderly people with muscle loss, or those with certain medical conditions.
Can BMI predict my health risks?
BMI is a useful screening tool that correlates with health risks, but it's not diagnostic. Your overall health depends on many factors including fitness level, diet quality, genetics, and lifestyle habits.
What's the difference between BMI and body fat percentage?
BMI measures weight relative to height, while body fat percentage measures the proportion of fat to total body weight. Body fat percentage provides more detailed body composition information but requires specialized equipment to measure accurately.
Start Your Health Journey Today
Understanding your BMI is the first step toward better health. Use our free calculator above to get instant results, then take action based on your findings. Remember, small consistent changes lead to lasting improvements in your overall wellness.
Ready to calculate your BMI? Simply enter your height and weight in the calculator above for immediate results and personalized recommendations.
Why Choose Our BMI Calculator?
Advanced features to support your health journey
Personalized Recommendations
Get tailored diet and exercise plans based on your specific BMI category and goals.
Progress Tracking
Save and track your BMI calculations over time to monitor your health journey.
100% Private
All calculations are done locally in your browser. Your data never leaves your device.
Mobile Friendly
Works perfectly on all devices - desktop, tablet, and mobile. Calculate anywhere, anytime.
Multi-Unit Support
Switch seamlessly between metric (kg/cm) and imperial (lb/ft) measurement systems.
Instant Results
Get immediate BMI calculations with visual gauge and comprehensive health insights.
Important Medical Disclaimer
Consult Healthcare Professionals: BMI is a screening tool, not a diagnostic instrument. For personalized health advice, weight management plans, or concerns about your BMI results, always consult with qualified healthcare providers, registered dietitians, or certified fitness professionals.
Individual Variations: BMI may not accurately reflect health status for athletes, elderly individuals, pregnant women, or people with certain medical conditions. Your healthcare provider can help interpret your results in the context of your overall health.