BMI is your weight in kilograms divided by your height in metres squared (kg/m²). Enter your height and weight above and the calculator does the maths for you, then matches your result to the World Health Organization weight categories.1

The formula is simple, which is its strength and its weakness: it’s easy to track over time, but it can’t tell the difference between fat and muscle.

BMI is a population screening tool, so it can be misleading for individuals. Because it only uses height and weight, a very muscular person can register as “overweight” while carrying little fat, and an older person who has lost muscle can register as “healthy” while carrying excess fat.

It also doesn’t show where fat sits, which is one of the most important factors for health. For these reasons, leading bodies now advise that obesity should not be judged on BMI alone, but alongside a measure of waist size.²

First, take a breath: a single number doesn’t define your health, and risk can improve with changes that are smaller and more achievable than most people expect. Improving fitness and trimming your waist lower health risks even when the scale moves slowly.³
Second, you don’t have to plan this alone. A conversation with a doctor can help, who can look at your full picture and talk through the options that fit you.

Carrying excess body fat especially around the abdomen gradually adds strain to the heart, blood vessels and metabolism. Over time this raises the risk of conditions such as type 2 diabetes, high blood pressure, heart disease, sleep apnoea and joint problems. ^1,2
The encouraging part: risk is not fixed. Even modest changes in fitness and waist size can meaningfully lower these risks, often before the number on the scale moves much at all. ²