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BMI calculator

BMI, or body mass index, is one way of measuring whether you’re a healthy weight for your height.

The result gives an indication of whether you’re a healthy weight for how tall you are, and if not, how over or underweight you are. BMI isn’t always the best measure to use because there are other things that you need to consider when it comes to weight (see our limitations information further down the page). But it can be a useful guide.

Simply enter your details into our calculator to find out what your BMI is and whether you’re a healthy weight.

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What your BMI result means

You’re in the underweight range, with a BMI score of under 18.5.

If you’re underweight, you may not be getting all the nutrients that your body needs. Different nutrients come from different foods; some give you energy and others help your body to grow, repair itself and function properly. Being underweight is sometimes associated with health conditions such as osteoporosis and fertility problems.

Your weight is determined by lots of factors. This includes how much energy (calories) you consume through food and how much energy your body uses. Aim for three balanced meals a day, making sure you eat enough carbohydrates and protein, with some healthy, nutrient-dense snacks in between. Good examples of nutrient-dense snacks include a handful of unsalted nuts, a pot of yogurt or peanut butter on toast. Talk to your practice nurse or GP for more advice. You may also be referred to a dietitian.

If your GP has any concerns about your health or wants to explore potential reasons for your weight loss, they may refer you for further tests or investigation. If you suffer with an eating disorder, your nurse or GP will be able to support you to gain the right treatment.

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What your BMI result means

A BMI score of between 18.5 and 24.9 is classed as a ‘healthy weight’.

Being a healthy weight can reduce your risk of developing health problems in the future, such as healthy weight and type 2 diabetes. Try to eat a healthy diet that is lower in fat and sugar and includes plenty of fruits and vegetables. We should also all aim to do some physical activity, ideally around 30 minutes a day on five days a week.

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What your BMI result means

A BMI score of between 25 and 29.9 is classed as ‘overweight’.

This category of BMI is associated with a higher risk of health conditions, such as high blood pressure, heart disease and certain types of cancer.

Your weight is determined by lots of factors. This includes how much energy (calories) you consume through food and how much energy your body uses. Try to eat a healthy balanced diet and get some exercise.

A healthy diet should include plenty of fruits and vegetables and be lower in fat and sugar. We should also all aim to do some physical activity, ideally around 30 minutes a day on five days a week. If you’ve not done much exercise before, you can start small. Consider walking to the shops instead of taking the car or use your lunch break to get outside and stretch your legs. Talk to a doctor or a dietitian for advice and more information.

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What your BMI result means

A BMI score of over 30 is classed as ‘obese’.

This category of BMI is associated with a higher risk of health conditions, such as heart disease, high blood pressure, cancer and type 2 diabetes.

Your weight is determined by lots of factors. This includes how much energy (calories) you consume through food and how much energy your body uses. Try to eat a healthy balanced diet and get some exercise.

A healthy diet should include plenty of fruits and vegetables and be lower in fat and sugar. We should also all aim to do some physical activity, ideally around 30 minutes a day on five days a week. If you’ve not done much exercise before, you can start small. Consider walking to the shops instead of taking the car or use your lunch break to get outside and stretch your legs. Talk to a doctor or a dietitian for advice and more information.

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  • Limitations of BMI Limitations of BMI

    Although, in general, BMI is a useful measure of whether or not you’re a healthy weight, it isn’t suitable for everyone. There are some groups of people where a BMI result should be considered carefully, or where it may not even be helpful to use at all.

    • Girls and boys develop differently and have different amounts of body fat at different ages. Therefore, a child’s age and sex are taken into account when looking at their BMI.
    • As we age, we tend to have more body fat and less muscle, so BMI may underestimate body fat in older people.
    • Athletes and people with a lot of muscle may have a high BMI but actually not have much body fat.
    • Pregnant women gain weight as a result of their developing baby. However, it’s still preferable to have a healthy BMI before becoming pregnant to reduce health risks to both you and your developing baby.
    • People from certain Black and Asian backgrounds are at risk of certain health problems at a lower BMI than others. Speak to your GP or practice nurse for more information.
  • Sources Sources

    • Body mass index – BMI. World Health Organization. www.euro.who.int, accessed 09 March 2021
    • Obesity: identification, assessment and management. National Institute for Health & Care Excellence. www.nice.org.uk, published 27 November 2014
    • Healthy Eating: Food Fact Sheet. British Dietetic Association. www.bda.uk.com, updated August 2020
    • Bone health checklist. The Royal Osteoporosis Society. www.theros.org.uk, accessed 09 March 2021
    • Underweight and fertility when planning a pregnancy. Tommy’s. www.tommys.org, updated 05 June 2018
    • Healthy snacks: Food Fact Sheet. British Dietetic Association. www.bda.uk.com, updated September 2018
    • Help and Treatment. Beat. www.beateatingdisorders.org.uk, last updated December 2020
    • Health matters: obesity and the food environment. Public Health England. www.gov.uk, published 31 March 2017
    • Macronutrients and energy balance. Oxford Handbook of Nutrition and Dietetics (3rd ed). Oxford Medicine Online. www.oxfordmedicine.com, April 2020
    • UK Chief Medical Officers' Physical Activity Guidelines. Department of Health and Social Care. www.gov.uk, published 7 September 2019
    • Body mass index: Considerations for Practitioners. Centers for Disease Control and Prevention. www.cdc.gov, accessed 09 March 2021
    • Weight management before, during and after pregnancy. National Institute for Health & Care Excellence. www.nice.org.uk, published 28 July 2010
  • Author information Author information

    Reviewed by Abbey Stanford, Specialist Heath Editor, Bupa Health Content Team, March 2021
    Expert reviewer, Niamh Hennessy, Lead Dietitian, Cromwell Hospital
    Next review due March 2024


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