What's your BMI?

Being underweight could be a sign that you're not eating enough or you may be ill. If you are underweight, you should visit your GP for further help and advice.

For further information on underweight adults visit the NHS website

A healthy weight result means your BMI is within the range it should be for your height. You should try to maintain this weight.

For tips on maintaining your weight visit the NHS website

An overweight result means you should try to lose some weight. The best way to lose weight is through a combination of diet and exercise. The BMI calculator will give you a personal calorie allowance to help you achieve a healthy weight safely.

An obese result means you should try to lose some weight. The best way to lose weight if you're obese is through a combination of diet and exercise, and, in some cases, medication. Contact your GP for help and advice.

Black, Asian and other minority ethnic groups have a higher risk of developing some chronic conditions, such as type 2 diabetes.

These adults with a BMI of:

• 23 or more are at increased risk
• 27.5 or more are at high risk

Measuring your waist is a good way to check you're not carrying too much fat around your stomach, which can raise your risk of heart disease, type 2 diabetes and stroke.

You can have a healthy BMI and still have excess tummy fat – meaning you're still at risk of developing these conditions.

Regardless of your height or BMI, you should try to lose weight if your waist is:

• 94cm (37 inches) or more for men
• 80cm (31.5 inches) or more for women

You are at very high risk and should contact your GP if your waist is:

• 102cm (40 inches) or more for men
• 88cm (34 inches) or more for women

For children and young people aged 2 to 18, the BMI calculator takes into account age and gender as well as height and weight.

Overweight children are thought to be at increased risk of a variety of health conditions, and they're also more likely to be overweight as adults.

Measuring waist size isn't routinely recommended for children because it doesn't take their height into account.

Contact your GP if you're concerned about your child's weight. They may be able to refer you to your local healthy lifestyle programme for children, young people and families.

For further information on underweight children aged 6 to 12 visit the NHS website 

Your BMI can tell you if you're carrying too much weight, but it can't tell if you're carrying too much fat.

The BMI can't tell the difference between excess fat, muscle, or bone.

The adult BMI doesn't take into account age, gender or muscle mass.

This means:

• Very muscular adults and athletes may be classed "overweight" or "obese" even though their body fat is low
• Adults who lose muscle as they get older may fall into the "healthy weight" range even though they may be carrying excess fat

Pregnancy will also affect a woman's BMI result – your BMI will go up as your weight increases. You should use your pre-pregnancy weight when calculating your BMI.

Apart from these limitations, the BMI is a relatively straightforward and convenient way of assessing someone's weight.