BMI Calculator

Understanding your BMI result

Underweight

Being underweight could be a sign you're not eating enough or you may be ill. If you're underweight, a GP can help.

Find out more in underweight adults

Healthy weight

Keep up the good work! For tips on maintaining a healthy weight, check out the food and diet and fitness sections.

Overweight

The best way to lose weight if you're overweight 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.

Obese

The best way to lose weight if you're obese is through a combination of diet and exercise, and, in some cases, medicines. See a GP for help and advice.

Black, Asian and other minority ethnic groups

Black, Asian and other minority ethnic groups have a higher risk of developing some long-term (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

Why waist size also matters

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.

To measure your waist:

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

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

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

You're at very high risk and should contact a GP if your waist is:

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

Children's BMI

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.

The BMI calculator works out if a child or young person is:

• underweight – on the 2nd centile or below
• healthy weight – between the 2nd and 91st centiles
• overweight – 91st centile or above
• very overweight – 98th centile or above

A child's BMI is expressed as a "centile" to show how their BMI compares with children who took part in national surveys.

For example, a girl on the 75th centile is heavier than 75 out of 100 other girls her age.

Measuring waist size is not routinely recommended for children because it does not take their height into account.

See a 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.

Find out more in underweight children aged 6 to 12 and very overweight children.

Get tips on how to encourage your child to be more active and eat well

Limitations of the BMI

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

The BMI cannot tell the difference between excess fat, muscle or bone.

The adult BMI does not 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.

Eating disorders

If you have an eating disorder, the BMI calculator results do not apply. Please get further advice from a GP.

Next steps

You can use your BMI result as a starting point for further discussion with a GP about your weight and general health.

Find out how your GP can help you lose weight and check out the Change4Life website for practical tips on staying healthy as a family.

A BMI above the healthy weight range or too much fat around your waist can increase your risk of serious health problems like:

• heart disease
• type 2 diabetes
• stroke
• certain types of cancer