Doctors use body mass index (BMI) as a simple way to assess whether a patient needs to lose weight.

The calculation is based on comparing a person's weight with their body height. It applies equally to men and women.

To calculate your body mass index divide your weight in kilograms by the square of your height in metres.

Click here to calculate your Body Mass Index

A BMI of 25 to 29.9 is considered overweight and one 30 or above is considered obese.

People with BMIs between 19 and 22 live longest. Death rates are noticeably higher for people with indexes 25 and above.

The BMI is not infallable. For instance, it is possible for a healthy, muscular athlete with very low body fat to be classified obese using the BMI formula.

If you are a trained athlete, your weight based on your measured percent body fat would be a better indicator of what you should weigh.