The Body Mass Index (BMI) is a simple way to measure body size – estimating body fat and health risks based on height and weight. The BMI calculator classifies people as being underweight, normal, overweight, or obese.
Underweight
Being underweight could be a sign you're not eating enough or that you may be ill.
If you're underweight, contact your general practitioner for further evaluation.
Normal weight
The medical community recommends that you keep your weight within this range.
Overweight
People who fall into this category may be at risk of developing obesity. They might also be at risk of developing other health problems, or that their current health problems may worsen. The recommendation is to consult a healthcare provider trained in obesity management.
There are two recommendations for people who fall into the pre-obesity category, which are recommended by European23 and American24 clinical guidelines for obesity management in adults.
The recommendation for people with a BMI between 25.0 and 29.9 who do not have weight-related health problems (i.e. high blood pressure or high cholesterol) is to prevent further weight gain through healthy eating and increased physical activity.23
For people with a BMI between 27 and 29.0, who also have weight-related health problems, the recommendation is to lose weight by combining lifestyle interventions and anti-obesity medications to achieve weight loss and improve health and quality of life.23,24
Obesity I
People with a BMI of 30 or above may have obesity, which is defined as an abnormal or excessive accumulation of fat25 that may harm health. Today, a number of health organisations recognise obesity as a chronic, but manageable disease.23
The World Health Organisation and other health organisations distinguish three classes of obesity:
Obesity Classification BMI
Class 30.0–34.9
Class 35.0–39.9
Class III Above 40
The BMI ranges are based on the effect that excessive body fat has on individuals’ health, life expectancy and risk of developing diseases. As BMI increases, so does the risk for some diseases.26
It’s recommended that people with a BMI of 30 or above consult a healthcare provider trained in obesity management for diagnosis, risk assessment and treatment of obesity and weight-related health complications.
The goal of managing and treating obesity is not simply to lose weight, but instead to improve health and lower the risks of other health complications. Even losing as little as five percent of body weight – and maintaining this weight loss – can improve overall wellbeing, while also reducing the risk of weight-related complications.27
There’s a range of scientifically proven treatment options for obesity that may be recommended depending on individual needs, health status and the presence or absence of weight-related complications. Treatment may include a combination of the following options*:
Healthy Eating
Increased physical activity
Behavioural therapy
Meal replacements / low energy diets
* Disclaimer: This information is not a substitute for the advice of a healthcare provider. If you have any questions regarding your health, you should contact your general practitioner or another qualified healthcare provider.
Obesity II
People with a BMI of 30 or above may have obesity, which is defined as an abnormal or excessive accumulation of fat25 that may harm health. Today, a number of health organisations recognise obesity as a chronic, but manageable disease.23
The World Health Organisation and other health organisations distinguish three classes of obesity:
Obesity Classification BMI
Class 30.0–34.9
Class 35.0–39.9
Class III Above 40
The BMI ranges are based on the effect that excessive body fat has on individuals’ health, life expectancy and risk of developing diseases. As BMI increases, so does the risk for some diseases.26
It’s recommended that people with a BMI of 30 or above consult a healthcare provider trained in obesity management for diagnosis, risk assessment and treatment of obesity and weight-related health complications.
The goal of managing and treating obesity is not simply to lose weight, but instead to improve health and lower the risks of other health complications. Even losing as little as five percent of body weight – and maintaining this weight loss – can improve overall wellbeing, while also reducing the risk of weight-related complications.27
There’s a range of scientifically proven treatment options for obesity that may be recommended depending on individual needs, health status and the presence or absence of weight-related complications. Treatment may include a combination of the following options*:
Healthy Eating
Increased physical activity
Behavioural therapy
Meal replacements / low energy diets
* Disclaimer: This information is not a substitute for the advice of a healthcare provider. If you have any questions regarding your health, you should contact your general practitioner or another qualified healthcare provider.
Obesity III
People with a BMI of 30 or above may have obesity, which is defined as an abnormal or excessive accumulation of fat25 that may harm health. Today, a number of health organisations recognise obesity as a chronic, but manageable disease.23
The World Health Organisation and other health organisations distinguish three classes of obesity:
Obesity Classification BMI
Class I 30.0–34.9
Class II 35.0–39.9
Class II Above 40
The BMI ranges are based on the effect that excessive body fat has on individuals’ health, life expectancy and risk of developing diseases; as BMI increases, so does the risk for some diseases.26
It’s recommended that people with a BMI of 30 or above consult a healthcare provider trained in obesity management for diagnosis, risk assessment and treatment of obesity and weight-related health complications.
The goal of managing and treating obesity is not simply to lose weight, but instead to improve health and lower the risks of other health complications. Even losing as little as five percent of body weight – and maintaining this weight loss – can improve overall wellbeing, while also reducing the risk of weight-related complications.27
There’s a range of scientifically proven treatment options for obesity that may be recommended depending on individual needs, health status and the presence or absence of weight-related complications. Treatment may include a combination of the following options*:
Healthy Eating
Increased physical activity
Behavioural therapy
Meal replacements / low energy diets
* Disclaimer: This information is not a substitute for the advice of a healthcare provider. If you have any questions regarding your health, you should contact your general practitioner or another qualified healthcare provider.
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BMI calculator: Check your BMI now
The BMI calculator divides your weight in kg by square of height in
meters. See where your result fits among the BMI classes below. Click
on a BMI class to learn more.
Classification |
BMI is expressed in kg/m2 |
Below 18.5 | |
18.5-24.9 | |
25.0-29.9 | |
30 and above | |
30.0-34.9 | |
35.0-39.9 | |
| 40 and above |
*This BMI calculator is for adults 20 years or older. Talk to your doctor about your BMI if you're under the age of 20.
Why is BMI important to know?
BMI is a good way to check your risk of diseases related to body fat. Living with overweight or obesity is associated with other diseases and an increased mortality risk.1 Generally, the higher your BMI, the greater the risk of developing other chronic obesity-related diseases, including:
- Type 2 diabetes2
- Cardiovascular diseases3, such as coronary heart disease4
- Stroke & MI5
- High blood pressure6
- Infertility7
- Depression8 and anxiety9
- Dyslipidemia10
- Non-alcoholic fatty liver disease (NAFLD)/Non-alcoholic steatohepatitis (NASH)11
- Gastroesophageal reflux disease (GERD)12
- Metabolic syndrome (MetS)13
- Urinary incontinence14
- Obstructive sleep apnea and breathing problems15
- Chronic kidney disease16
- Various types of cancer: including (but not limited to) breast, colon, endometrial, oesophageal, kidney, ovarian, and pancreatic cancer17
- Knee osteoarthritis18
- Gallstone disease19
- Thrombosis20
- Gout21
- Increased risk of mortality compared to those with a healthy BMI22
Ask your doctor for more information about any of these diseases and how they relate to your BMI.
What are the limits of BMI?
BMI is a simple and objective measurement, but it can be misleading in certain cases and for some groups of people. Research has shown that BMI is less accurate in predicting the risk of disease in older people, athletes, those who are tall or short, and those with more muscular body types. For example, elite athletes or bodybuilders have more muscle and weigh more, which makes their BMI higher.
BMI ranges vary across different regions and populations. For example, the cut-off ranges for Indian and Japanese populations differ to those for western populations.
BMI also doesn't take into account:
- Hereditary risk factors associated with obesity-related diseases, such as metabolic syndrome
- Environmental and lifestyle factors other than obesity that can contribute to your risk of developing chronic diseases
- How body fat is distributed in individuals
It's important to remember that living with obesity doesn't necessarily mean you're unhealthy, just as being at a ‘normal’ weight doesn't necessarily mean you're healthy. Your BMI doesn't define you – but understanding your BMI can be a useful tool for taking charge of your health.
Regardless of your BMI, healthcare professionals recommend a healthy diet and lifestyle. Talk to your doctor about your weight and evaluate what actions may be needed.
References
- Abdelaal M, le Roux CW, Docherty NG. Morbidity and mortality associated with obesity. Ann Transl Med. 2017 Apr;5(7):161. doi: 10.21037/atm.2017.03.107. PMID: 28480197; PMCID: PMC5401682.
- Hussain, A et al, “Type 2 Diabetes and obesity: A review” Journal of Diabetology, June 2010; 2:1
- Katzmarzyk, P T et al, “Body mass index and risk of cardiovascular disease, cancer and all-cause mortality” Can. J. Public Health, vol. 103, no. 2, pp. 147–151, 2012, doi:10.1007/BF03404221.
- Lamon-Fava, S et al, “Impact of Body Mass Index on Coronary Heart Disease Risk Factors in Men and Women,” Arterioscler. Thromb. Vasc. Biol., vol. 16, no. 12, pp. 1509–1515, Dec. 1996, doi: 10.1161/01.ATV.16.12.1509.
- Kurth, T et al, “Prospective Study of Body Mass Index and Risk of Stroke in Apparently Healthy Women,” Circulation, vol. 111, no. 15, pp. 1992–1998, Apr. 2005, doi:10.1161/01.CIR.0000161822.83163.B6.
- Landi, F et al, “Body Mass Index is Strongly Associated with Hypertension: Results from the Longevity Check-Up 7+ Study” Nutrients. 2018 Dec; 10(12): 1976. Published online 2018 Dec 13. doi: 10.3390/nu10121976
- Dağ, Z Ö et al, “Impact of obesity on infertility in women,” J. Turkish Ger. Gynecol. Assoc., vol. 16, no. 2, pp. 111–117, Jun. 2015, doi: 10.5152/jtgga.2015.15232.
- Moussa, O M et al, “Effect of body mass index on depression in a UK cohort of 363037 obese patients: A longitudinal analysis of transition,” Clin. Obes., vol. 9, no. 3, p. e12305, Jun. 2019, doi: https://doi.org/10.1111/cob.12305.
- Zhao, G et al, “Depression and anxiety among US adults: associations with body mass index,” Int. J. Obes., vol. 33, no. 2, pp. 257–266, 2009, doi: 10.1038/ijo.2008.268.
- Van Hemelrijck, M et al, “Longitudinal study of body mass index, dyslipidemia, hyperglycemia, and hypertension in 60,000 men and women in Sweden and Austria” Published: June 13, 2018https://doi.org/10.1371/journal.pone.0197830
- Loomis, A K et al, “Body Mass Index and Risk of Nonalcoholic Fatty Liver Disease: Two Electronic Health Record Prospective Studies,” J. Clin. Endocrinol. Metab., vol. 101, no.3, pp. 945–952, Mar. 2016, doi: 10.1210/jc.2015-3444.
- Zafar, S et al, “Correlation of gastroesophageal reflux disease symptoms with body mass index,” Saudi J. Gastroenterol., vol. 14, no. 2, pp. 53–57, Apr. 2008, doi: 10.4103/1319-3767.39618.
- Han, T S et al, “A clinical perspective of obesity, metabolic syndrome and cardiovascular disease,” JRSM Cardiovasc. Dis., vol. 5, pp. 2048004016633371–2048004016633371, Feb. 2016, doi: 10.1177/2048004016633371.
- Subak, L L et al, “Obesity and Urinary Incontinence: Epidemiology and Clinical Research Update” J Urol. 2009 Dec; 182(6 Suppl): S2–S7 doi: 10.1016/j.juro.2009.08.071
- Romero-Corral, A et al, “Interactions Between Obesity and Obstructive Sleep Apnea - Implications for Treatment” Chest. 2010 Mar; 137(3): 711–719. doi: 10.1378/chest.09-0360
- Herrington, W G et al, “Body-mass index and risk of advanced chronic kidney disease: Prospective analyses from a primary care cohort of 1.4 million adults in England,” PLoS One, vol. 12, no. 3, p. e0173515, Mar. 2017, [Online]. Available: https://doi.org/10.1371/journal.pone.0173515.
- Bhaskaran, K et al, “Body-mass index and risk of 22 specific cancers: a population-based cohort study of 5.24 million UK adults,” Lancet, vol. 384, no. 9945, pp. 755–765, Aug. 2014, doi: 10.1016/S0140-6736(14)60892-8.
- Zheng, H et al, “Body mass index and risk of knee osteoarthritis: Systematic review and meta-analysis of prospective studies,” BMJ Open, vol. 5, no. 12, 2015, doi: 10.1136/bmjopen-2014-007568.
- Su, Y P et al, “Strong association between metabolically-abnormal obesity and gallstone disease in adults under 50 years” BMC Gastroenterol 19, 117 (2019). https://doi.org/10.1186/s12876-019-1032-y
- Yang, G et al, “The effects of obesity on venous thromboembolism: A review” Open J Prev Med. 2012 Nov; 2(4): 499–509. doi: 10.4236/ojpm.2012.24069
- Bai, L et al, “Incident gout and weight change patterns: a retrospective cohort study of US adults” Arthritis Res Ther. 2021; 23: 69. Published online 2021 Mar 2. doi: 10.1186/s13075-021-02461-7
- Klatsky, A L et al, “Body Mass Index and Mortality in a Very Large Cohort: Is It Really Healthier to Be Overweight?,” Perm. J., vol. 21, pp. 16–142, 2017, doi: 10.7812/TPP/16-142.
- Yumuk, V et al, “European Guidelines for Obesity Management in Adults” Obes Facts. 2015 Dec; 8(6): 402–424. Published online 2015 Dec 5. doi: 10.1159/000442721
- Garvey, W T et al, “American Association of Clinical Endocrinologists and American College of Endocrinology comprehensive clinical practice guidelines for medical care of patients with obesity.” Endocrine Practice 2016;22:1–203.
- Rueda-Clausen, C F et al, “Assessment of People Living with Obesity,” Can. Adult Obes. Clin. Pract. Guidel., pp. 1–17, 2020, [Online]. Available: http://obesitycanada.ca/wpcontent/uploads/2020/09/6-Obesity-Assessment-v5-with-links.pdf
- Guh, D P et al, “The incidence of co-morbidities related to obesity and overweight: A systematic review and meta-analysis,” BMC Public Health, vol. 9, no. 1, p. 88, 2009, doi:10.1186/1471-2458-9-88.
- Ryan DH, Yockey SR. Weight Loss and Improvement in Comorbidity: Differences at 5%, 10%, 15%, and Over. Curr Obes Rep. 2017 Jun;6(2):187-194. doi: 10.1007/s13679-017-0262-y. PMID: 28455679; PMCID: PMC5497590.