BMI uses your height and weight to work out if you’re a healthy weight, underweight or overweight. Your BMI result is not the perfect measure of your overall health. It can’t tell if you’re carrying too much fat or you’ve got a lot of muscle. You could use your BMI result as a starting point for further discussion with your GP. The adult BMI doesn’t take into account age, sex or muscular build. This means that:

• Older adults can have a healthy BMI but still have too much fat. This is because older adults tend to have more body fat than younger adults.
• Women can have a healthy BMI but still have too much fat. This is because women tend to have more body fat than men with the same BMI.
• If you’re from a black and ethnic minority group, you’re at increased risk of type 2 diabetes with a BMI of 23 or more.
• An athletic adult with a lot of muscle may have a high BMI but not be overweight. This is because BMI can’t tell the difference between fat and muscle.

Taking these limitations into account, the BMI is a relatively straightforward and convenient way of initially assessing someone’s weight. If you are pregnant, you should use your pre-pregnancy weight to work out your BMI. Using your pregnancy weight may not be accurate.

Measuring your waist to height ratio can tell you if you have excess tummy fat, even if you have a healthy BMI.

To calculate your waist to height ratio, measure your waist and divide it by your height. Use measurements in the same units (for example, centimetres or inches).

A waist to height ratio of 0.5 or higher means you may have increased health risks such as heart disease, type 2 diabetes and stroke.

To measure your waist:

1. Find the bottom of your ribs and the top of your hips (just above your belly button).
2. Wrap a tape measure around your waist midway between these points.
3. Breathe out naturally before taking the measurement.