Body Mass Index (BMI) can be used to tell how healthy your weight is and to find out if you're a healthy weight for your height.
If you know your height and weight, enter it into the BMI calculator to find out how you score.
What is a healthy BMI?
For most adults, an ideal BMI is in the range 18.5 to 24.9.
If your BMI is 25 or more, you’re over the ideal weight for your height:
- 25 to 29.9 is overweight
- 30 to 39.9 is obese
- 40 or more is very obese
If your BMI is less than 18.5, you're under the ideal weight for your height.
If you want to calculate your BMI, see How can I work out my BMI? or try our healthy weight calculator.
These ranges are only for adults. BMI is interpreted differently for children. If you’re concerned about your child’s weight, get advice from your GP.
Overweight BMI
If your BMI is 25 or more, you should think about losing weight.
Being overweight or obese can increase your risk of health problems, such as:
- heart disease
- stroke
- type 2 diabetes
- some types of cancer
- high blood pressure (hypertension)
- kidney disease
Healthcare professionals use the words obese and obesity as clinical terms to indicate your increased risk of health problems. They do not use these terms to describe what you look like. You can find more information about obesity in the Health A-Z.
Talk to your GP before starting a weight loss programme if you have a long-term health condition, such as type 2 diabetes or heart failure.
If you intend to go on a low-fat or low-calorie diet to achieve gradual weight loss, you should seek advice from your GP beforehand.
Your GP can offer you help, support and advice before you start your diet. During your diet, you should also have regular follow-up appointments with your GP, to keep track of your progress. They can also offer support to help you achieve your weight-loss goal sensibly.
Underweight BMI
If your BMI is less than 18.5, you may want to talk to your GP about gaining weight.
Being underweight can increase your risk of other health problems, such as:
- brittle bones (osteoporosis)
- iron deficiency (anaemia)
For more information, see How can I gain weight safely?
Accuracy of BMI
As well as measuring your BMI, your healthcare professional may take other factors into account when assessing if you’re a healthy weight.
Muscle weighs more than fat. Very muscular people, such as heavyweight boxers, weight trainers and athletes, may be a healthy weight even though their BMI is classed as obese.
Your ethnic group can affect your risk of some health conditions. For example, adults of Asian origin may have a higher risk of health problems at BMI levels below 25.
You should not use BMI as a measure if you’re pregnant. Get advice from your midwife or GP if you’re concerned about your weight.
Your waist size
Carrying too much weight around your middle increases your risk of conditions such as coronary heart disease, high blood pressure and diabetes.
If you’re overweight, your healthcare professional may measure your waist as well as checking your BMI, to assess your risk of health problems.
For more information, see Why is my waist size important?
Read the answers to common health questions about exercise.
Further information:
Last reviewed: 15/09/2011
