BMI Calculator
| Category | BMI Range | Health Risk (NHS) |
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This BMI calculator follows the classification system recommended by the NHS (National Health Service) and the World Health Organization (WHO) for adults aged 18 and over.
What is BMI?
Body Mass Index (BMI) is a measure of body fat based on height and weight. It's a simple, inexpensive screening tool used by healthcare professionals worldwide, including the NHS, to identify potential weight issues that may lead to health problems.
BMI Formula
Metric Formula: BMI = weight (kg) ÷ height (m)²
Imperial Formula: BMI = (weight (lbs) ÷ height (in)²) × 703
BMI Categories (NHS / WHO Classification)
- Underweight: BMI less than 18.5 — Increased risk of nutritional deficiency and osteoporosis
- Healthy weight: BMI 18.5 – 24.9 — Lowest health risk
- Overweight: BMI 25 – 29.9 — Increased risk of heart disease, type 2 diabetes
- Obesity Class I: BMI 30 – 34.9 — Moderate risk of health complications
- Obesity Class II: BMI 35 – 39.9 — High risk of serious health conditions
- Obesity Class III: BMI 40 or greater — Very high risk of severe health issues
Why Use Our BMI Calculator?
- ✅ 100% Free — No hidden fees or subscriptions
- ✅ No Registration — Use instantly without creating an account
- ✅ Metric & Imperial units supported — Switch between kg/cm and lbs/in
- ✅ Instant results with NHS health risk assessment
- ✅ Mobile friendly — Works perfectly on any device
- ✅ Accurate calculations using WHO/NHS standards
Understanding Your BMI Result
Your BMI score places you into one of six categories ranging from underweight to obesity class III. While BMI is a useful screening tool, it's important to remember that it's not a diagnostic tool. The NHS recommends using BMI as a starting point for understanding your weight status.
Limitations of BMI
BMI does not account for muscle mass, bone density, overall body composition, or fat distribution. Athletes and individuals with high muscle mass may have a high BMI without being overweight. Pregnant women, elderly adults, and children under 18 require different assessment methods. For accurate health assessment, always consult a healthcare professional.
NHS Healthy Weight Advice
- 🥗 Eat a balanced diet rich in fruits, vegetables, and whole grains
- 🏃 Engage in regular physical activity — at least 150 minutes per week
- 💧 Stay hydrated with water instead of sugary drinks
- 😴 Get adequate sleep (7-9 hours per night)
- 📊 Monitor your weight regularly
- 👨⚕️ Consult your GP if you have concerns about your weight
Frequently Asked Questions
- What is a healthy BMI? — A healthy BMI for most adults is between 18.5 and 24.9.
- Is BMI accurate for everyone? — BMI is a screening tool, not a diagnostic tool. It may not be accurate for athletes, pregnant women, or elderly adults.
- Does BMI apply to children? — Children and teenagers use different BMI centile charts. This calculator is for adults aged 18+.
- What is the NHS recommendation for weight loss? — The NHS recommends a combination of healthy eating and regular physical activity for sustainable weight loss.
- Should I worry about my BMI? — BMI is a guide. If you're concerned about your weight, speak with your GP for personalized advice.