What is BMI?
Body mass index (BMI) is an estimate of body fat based on height and weight. It doesn’t measure body fat directly but instead uses an equation to make an approximation. BMI can help determine whether a person is at an unhealthy or healthy weight.
A high BMI can be a sign of too much fat on the body, while a low BMI can be a sign of too little fat on the body. The higher a person’s BMI, the greater their chances of developing certain serious conditions, such as heart disease, high blood pressure, and diabetes. A very low BMI can also cause health problems, including bone loss, decreased immune function, and anaemia.
While BMI can be useful in screening children and adults for bodyweight problems, it does have its limits. BMI may overestimate the amount of body fat in athletes and other people with very muscular bodies. It may also underestimate the amount of body fat in older adults and other people who have lost muscle mass.
Body Mass Index Formula
BMI is calculated by dividing a person’s weight by the square of their height.
Body Mass Index for Adults
Adults age 20 and older can interpret their BMI based on the following standard weight status categories. These are the same for men and women of all ages and body types:
| BMI | Weight Status |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obese |
Body Mass Index for Children
BMI is interpreted differently for people under age 20. While the same formula is used to determine BMI for all age groups, the implications for children and adolescents can vary depending on age and gender. The amount of body fat changes with age. It’s also different in young boys and girls. Girls usually acquire a higher amount of body fat and develop it earlier than boys.
The following table shows the percentile range for each weight status:
| Percentile | Weight Status |
|---|---|
| Below 5th | Underweight |
| 5th to 85th | Normal or healthy weight |
| 85th to 95th | Overweight |
| 95th and above | Obese |
