Body Mass Index (BMI) is a widely used measurement that helps assess whether an individual’s weight is within a healthy range based on their height. It is a screening tool used by the NHS, doctors, and health professionals to evaluate potential weight-related health risks.
Maintaining a healthy BMI is essential in preventing conditions such as heart disease, diabetes, and obesity-related illnesses. While BMI is not a perfect measure of health, it provides a quick and general assessment of whether a person is underweight, at a healthy weight, overweight, or obese.
BMI is a numerical value calculated from a person’s height and weight. It is used to determine if an individual is:
✔ Underweight
✔ Within a healthy weight range
✔ Overweight
✔ Obese
However, BMI does not measure body fat directly. Instead, it provides an estimate of body weight relative to height, which can help identify potential health risks associated with weight categories.
Learn more about BMI accuracy: How Accurate is BMI?
BMI is determined using the following formulas:
BMI = Weight (kg) ÷ Height (m²)
BMI = (Weight (lbs) ÷ Height (inches²)) × 703
| Height & Weight | Metric BMI Calculation | Imperial BMI Calculation |
|---|---|---|
| 170 cm, 70 kg | 70 ÷ (1.7 × 1.7) = 24.2 | - |
| 5ft 6in, 154 lbs | - | (154 ÷ 66²) × 703 = 24.8 |
Want to check your BMI instantly? Use the NHS BMI Calculator
According to NHS guidelines, BMI results are classified into the following categories:
| BMI Range | Category | Health Risk |
|---|---|---|
| Below 18.5 | Underweight | Increased risk of malnutrition, weakened immunity |
| 18.5 – 24.9 | Healthy Weight | Lowest health risk |
| 25 – 29.9 | Overweight | Increased risk of heart disease and high blood pressure |
| 30 and above | Obese | High risk of diabetes, stroke, joint problems |
View the complete NHS BMI classification: NHS BMI Chart
Being underweight may indicate:
✔ Nutritional deficiencies
✔ Weakened immune system
✔ Increased risk of osteoporosis
✔ Increase nutrient-dense foods
✔ Follow an NHS-approved weight gain plan
Read more: How to Gain Weight Safely
A high BMI is linked to:
✔ Increased risk of heart disease and diabetes
✔ High blood pressure and cholesterol levels
✔ Joint and mobility issues
✔ Follow a balanced diet and NHS-approved exercise routine
✔ Start an NHS-recommended weight loss programme
See NHS guidance on reducing BMI: How to Reduce BMI
BMI does not differentiate between muscle and fat. Athletes and bodybuilders may have a higher BMI due to muscle mass, even though they have low body fat levels.
Find alternative health measurements: BMI vs Body Fat Percentage
Children and teenagers: BMI is measured using growth percentiles rather than a fixed scale.
Older adults: Muscle loss in seniors affects BMI accuracy.
Age-specific BMI considerations: BMI for Children | BMI for Over 60s
BMI is not a reliable indicator during pregnancy due to weight fluctuations. The NHS focuses on healthy weight gain recommendations instead.
Learn more: BMI & Pregnancy
The NHS relies on BMI because:
✔ It is a quick and cost-effective screening tool.
✔ It helps identify individuals at risk of weight-related diseases.
✔ It is widely used in clinical and public health research.
BMI is often combined with waist-to-hip ratio measurements to get a better understanding of overall health risks.
Try the NHS Waist-to-Hip Ratio Calculator: Waist-to-Hip Ratio Calculator
BMI provides a general weight assessment, but it does not measure body composition, muscle mass, or fat distribution.
Check the recommended BMI range based on height and weight.
✔ Follow a healthy diet and NHS-approved exercise plan.
✔ Reduce processed foods and sugar intake.
See NHS weight loss strategies
✔ Increase healthy calorie intake with nutrient-dense foods.
