N.B. For an explanation of Body Mass Index and a discussion about its limitations and alternative weight measurement calculations see the section below the action plans.
BMI Action Plans:
Below 18.5 Underweight
If your BMI is less that 18.5 it is a strong indicator that you are underweight. To put on weight the only healthy method is to increase calorie intake and exercise more. A low body weight indicated a lack of healthy muscle tissue. Ensure that your diet is well balanced and consider increase protein intake to aid muscle growth.
Start exercising a few times a week with a combination of cardio workouts (running, swimming, sports), bodyweight circuit training workouts and fitness classes.
18.5 – 24.9 Normal
A BMI of 18.5 to 24.9 indicated that you are at a healthy weight. Well done, you are doing just fine. However, you may not be healthy, look to improve your diet and take regular exercise.
A healthy body weight is not always a fit and healthy body. If you are not fit and consuming too few calories then you may still be lacking in some essential nutrition as well as setting yourself up for longer term problems due to inactivity.
25.0 – 29.9 Overweight
A BMI of 25 to 29.9 suggests that you are overweight and are probably developing some belly fat. Unless you have built up a lot of muscle mass in recent years then there is a very good change that you need change your diet and exercise more to start burning off excess fat.
To lose weight you need to combine healthy diet and regular fitness activities. You do not need to join a gym although it can help. We have many suggestions for home fitness workouts and also advice on how to eat healthy. You may also want to consider following a weight loss plan. If you are looking for an effective diet solution then take a look at our Low GI Diet eBook.
30.0 + Obese
A BMI of over 30 indicates that you are obese. You really have to make some changes. You need to take urgent action to start losing fat and improving your fitness. Total lifestyle change is required. If you have not exercised for a long time then start easy with our walking for fitness plan and then move on to more intensive forms of fitness training.
Also read up on the basics of a healthy diet and start making changes to your diet to improve quality and reduce quantity. Also consider a low GI diet which will help you to control blood sugars and lose weight – Low GI Diet eBook.
Limitations of BMI
What does it mean to be overweight? Can we really calculate how overweight a person is? There are a few methods to determine whether or not you are overweight and while none are perfect they do all provide a good indication of whether or not you are healthy.
Body Mass Index is still the most commonly used calculation because it is so easy to measure – you just need to know your height and weight.
However, BMI does not take into consideration muscle:fat ratios, so male athletes can sometimes appear overweight on the scale while women with very little muscle mass may appear a “normal” weight when they are actually carrying too much fat.
For example, Arnold Schwarzenegger’s BMI is around 35 – based on a heigh of 178 cm and mass of 113 kg. He is certainly not obese or overweight.
Health professionals also use waist measurement, including waist-to-hip ratio, to determine if a person is carrying too much fat.
However, for simplicity we shall provide you with a body mass index calculator (just below this explanation).
We have also added a chart to provide a better visualization of obesity levels. At the end of the article there are also note on genetic / racial variations that should be considered.
What Is Body Mass Index (BMI)?
Body mass index (BMI) is a statistical measure of the weight of a person scaled according to height. It is a guide to how overweight or underweight a person is, but it should not be used in isolation to diagnose a weight problem.
While it can give a good answer to your question “Am I Overweight?“, it cannot provide a totally accurate answer is some circumstances – read below to learn more.
Many bodybuilders and athletes would be considered overweight according to the BMI calculation, as BMI does not take into account muscle mass, just total mass. As muscle is denser that fat, very muscular people can show a high BMI even though they are of a healthy weight.
It is generally considered that waist circumference is a better measure of how overweight a person is.
So to be healthy you really need to try to lose your belly fat and get a flat stomach, or at least get your waist below 36 inches. However, BMI is still a good indication of whether or not you are overweight.
The chart below provides a visual guide to BMI. Draw a line from your weight (in pounds at the top or kilos at the bottom) to your height (meters on the left or feet/inches on the right) and where the lines cross is your BMI. If you are in the yellow zone you are a healthy weight.
Please see below for some International variations on this scale and updated sub-categories from the World Health Organization.
World Health Organization New BMI Classification
The WHO have now provided more detailed classifications for BMI.
The International Classification of adult underweight, overweight and obesity according to BMI
|Principal cut-off points||Additional cut-off points|
|Moderate thinness||16.00 – 16.99||16.00 – 16.99|
|Mild thinness||17.00 – 18.49||17.00 – 18.49|
|Normal range||18.50 – 24.99||18.50 – 22.99|
|23.00 – 24.99|
|Pre-obese||25.00 – 29.99||25.00 – 27.49|
|27.50 – 29.99|
|Obese class I||30.00 – 34.99||30.00 – 32.49|
|32.50 – 34.99|
|Obese class II||35.00 – 39.99||35.00 – 37.49|
|37.50 – 39.99|
|Obese class III||≥40.00||≥40.00|
Source: Adapted from WHO, 1995, WHO, 2000 and WHO 2004.
Class 3 Obese is more commonly known as morbidly obese. When someone reaches a BMI of over 40 it becomes very likely that they will develop chronic health conditions such as Type 2 Diabetes and heart disease, plus also suffer from reduced mobility and a much poorer quality of life.
Many Class 3 individuals become house bound and suffer from depression which makes changes lifestyle and dietary habits next to impossible.
International BMI Variations
Many countries have changed the scale to suit the demographics of their people. All units in kg/m2.
Japan and Hong Kong
Japan and Hong Kong have lowered the thresholds for being overweight and obese as follows:
- Normal: 18.5 to 22.9
- Overweight: 23.0 to 24.9
- Obese 25.0: above
Signapore has added an additional category to classify the very underweight – Emaciation. They also make a BMI of over 40 officially morbidly obese;
- Emaciation: 14.9 or less
- Underweight: 15 to 18.4
- Normal: 18.5 to 22.9
- Overweight: 23 to 27.5
- Obese: 27.6 to 40
- Morbidly Obese: greater than 40
References and Further Resources on BMI
- BMI classification – World Health Organisation.
- “Big fat beat up” by Lousie Staley. IPA Review, Institute of Public Affairs (pdf file).
- “Adjusting athletes’ body mass index to better reflect adiposity in epidemiological research.” by Nevill AM, Winter EM, Ingham S, Watts A, Metsios GS, Stewart AD. Published in Journal of Sports Science. 2010;28(9):1009-16. Abstract.
- Know Your Risks – Singapore Health Promotion Board.
- “The paradox of low body mass index and high body fat percentage among Chinese, Malays and Indians in Singapore” by Deurenberg-Yap M, Schmidt G, van Staveren WA, Deurenberg P. Published in Int J Obes Relat Metab Disord. 2000 Aug;24(8):1011-7. Abstract.
- “Overweight Japanese with body mass indexes of 23.0-24.9 have higher risks for obesity-associated disorders: a comparison of Japanese and Mongolians.” by Shiwaku K, Anuurad E, Enkhmaa B, Nogi A, Kitajima K, Shimono K, Yamane Y, Oyunsuren T.. Published in Int J Obes Relat Metab Disord. 2004 Jan;28(1):152-8. Abstract.