BMI is determined by your weight in kg divided by your (height in metres)2. BMI estimates whether you are underweight, healthy weight, overweight or obese, based on your height and weight.

Doctors, dietitians and other health professionals use BMI as an indication of your risk of chronic disease. It is designed for men and women over the age of 18 and should not be used by pregnant women.

Why is a healthy BMI important?

Being overweight or obese increases your risk of several health problems, including:

  • type 2 diabetes;
  • stroke;
  • coronary heart disease and heart attack;
  • some types of cancer;
  • infertility and sexual problems; and
  • mental health problems, including depression, anxiety and psychological distress.

BMI is not suitable for everyone

BMI does not distinguish between weight due to muscle and weight due to fat, so it does not take into account differences in body composition. An elite sportsperson may have a high muscle mass, and a BMI above 25, but not be carrying excess body fat. Your doctor can advise you whether you are truly underweight.
BMI measures may not be suitable for all population groups.

  • Aboriginal people. Lower BMI cut-offs may be considered for Aboriginal people, whose healthy BMI range may be different from that for people of European descent. This is due to their relatively long legs in relation to weight, which is a factor known to influence BMI.
  • Asian people. Similarly, for Asian people, cut-off points for health risks appear to be lower than for people of European descent.
  • Pacific Islanders. For Pacific Islanders, including Maori and Torres Strait Islanders, higher BMI cut-off values may be considered. Always check with your doctor if you are concerned about your weight.

BMI classification

BMI of less than 18.5 Underweight
BMI of 18.5 – 24.9 Healthy weight
BMI of 25 – 29.9 Overweight
BMI of 30 or more Obese

Last Reviewed: 09/07/2019

myDr

1. Australian Government; National Health and Medical Research Council (NHMRC). Clinical practice guidelines for the management of overweight and obesity in adults, adolescents and children in Australia, Systematic Review. May, 2013. Melbourne: NHMRC. https://www.nhmrc.gov.au/about-us/publications/clinical-practice-guidelines-management-overweight-and-obesity (accessed July 2019).
2. Australian Government; National Health and Medical Research Council (NHMRC). Summary guide for the management of overweight and obesity in primary care. December 2013. Melbourne: NHMRC. https://www.nhmrc.gov.au/about-us/publications/clinical-practice-guidelines-management-overweight-and-obesity (accessed July 2019).
3. Cardiovascular disease risk modification [revised Jan 2019]. In: eTG complete. Melbourne: Therapeutic Guidelines Limited; 2019 June. Available at: http://www.tg.org.au (accessed July 2019).