Your body mass index (BMI) is a rough estimate of whether you are overweight. It’s harder to lose weight if you’re already a healthy BMI, as your body is trying to stay healthy.

To find your BMI, divide your weight in kilos (kg) by the square of your height in metres (m). So, if you’re 1.65m tall and weigh 57kg, your BMI is 57 divided by 2.72 (i.e 1.65 x 1.65). This equals just under 21. 

For women, a BMI under 19 is considered to be underweight, over 25 is overweight and over 30 is obese. Between 19 and 25 is healthy.