Reviewed by:
Nancy DeLuca, RDLast Updated:
In addition to showing you how to calculate your BMI, this page will cover why your score is important and the background of the BMI formula.
BMI Calculator
Your Weight Classification:
Below 18.5
Underweight
Your Health Risk:HighYou are considered to be underweight and should take physician-approved steps to gain weight.
18.5 – 24.9
Healthy Weight
Your Health Risk:Low25.0 – 29.9
Overweight
Your Health Risk:MODERATEYour risk increases to “High” if two or more of the following apply to you:
- You smoke cigarettes
- Family history of premature heart disease
- High blood glucose (blood sugar)
- High blood pressure (hypertension)
- Low HDL-cholesterol
(“good” cholesterol) - High LDL-cholesterol
(“bad” cholesterol) - High triglycerides
Your risk of health issues are even higher if your waist circumference is over 35 inches (88 cm) for women or 40 inches (102 cm) for men.
30.0 – 34.9
Obese
Your Health Risk:HighYou have a very high risk of obesity-related health problems.
Your risk is even higher if your waist circumference is over 35 inches (88 cm) for women or 40 inches (102 cm) for men.
Your BMI indicates that you may be a good candidate for weight loss surgery if you also have poorly controlled type 2 diabetes and/or have a higher risk of cardiovascular disease.
Learn Your Options35.0 – 39.9
Severely Obese
Your Health Risk:HighYou have a very high risk of obesity-related health problems.
Your risk is even higher if your waist circumference is over 35 inches (88 cm) for women or 40 inches (102 cm) for men.
Your BMI indicates that you may be a good candidate for weight loss surgery if you also have one or more obesity-related health problems.
Learn Your Options40.0 – 49.9
Morbidly Obese
Your Health Risk:HighYou have a very high risk of obesity-related health problems.
Your risk is even higher if your waist circumference is over 35 inches (88 cm) for women or 40 inches (102 cm) for men.
Your BMI indicates that you may be a good candidate for weight loss surgery.
Learn Your Options50 or Higher
Super Obese
Your Health Risk:HighYou have a very high risk of obesity-related health problems.
Your risk is even higher if your waist circumference is over 35 inches (88 cm) for women or 40 inches (102 cm) for men.
Your BMI indicates that you may be a good candidate for weight loss surgery.
Learn Your Options
Your Weight Classification:
Below 18.5
Underweight
Your Health Risk:HighYou are considered to be underweight and should take physician-approved steps to gain weight.
18.5 – 24.9
Healthy Weight
Your Health Risk:Low25.0 – 29.9
Overweight
Your Health Risk:MODERATEYour risk increases to “High” if two or more of the following apply to you:
- You smoke cigarettes
- Family history of premature heart disease
- High blood glucose (blood sugar)
- High blood pressure (hypertension)
- Low HDL-cholesterol
(“good” cholesterol) - High LDL-cholesterol
(“bad” cholesterol) - High triglycerides
Your risk of health issues are even higher if your waist circumference is over 35 inches (88 cm) for women or 40 inches (102 cm) for men.
30.0 – 34.9
Obese
Your Health Risk:HighYou have a very high risk of obesity-related health problems.
Your risk is even higher if your waist circumference is over 35 inches (88 cm) for women or 40 inches (102 cm) for men.
Your BMI indicates that you may be a good candidate for weight loss surgery if you also have poorly controlled type 2 diabetes and/or have a higher risk of cardiovascular disease.
Learn Your Options35.0 – 39.9
Severely Obese
Your Health Risk:HighYou have a very high risk of obesity-related health problems.
Your risk is even higher if your waist circumference is over 35 inches (88 cm) for women or 40 inches (102 cm) for men.
Your BMI indicates that you may be a good candidate for weight loss surgery if you also have one or more obesity-related health problems.
Learn Your Options40.0 – 49.9
Morbidly Obese
Your Health Risk:HighYou have a very high risk of obesity-related health problems.
Your risk is even higher if your waist circumference is over 35 inches (88 cm) for women or 40 inches (102 cm) for men.
Your BMI indicates that you may be a good candidate for weight loss surgery.
Learn Your Options50 or Higher
Super Obese
Your Health Risk:HighYou have a very high risk of obesity-related health problems.
Your risk is even higher if your waist circumference is over 35 inches (88 cm) for women or 40 inches (102 cm) for men.
Your BMI indicates that you may be a good candidate for weight loss surgery.
Learn Your Options
Required BMI for Weight Loss Surgery
30+ with health issues, 40+ without health issues
Required BMI for Weight Loss Surgery: 30+ with health issues, 40+ without health issues
If your body mass index is above 30, you may qualify for weight loss surgery.
Body Mass Index Body Mass Index |
30 to 34.9 30 to 34.9 |
35 to 40 35 to 40 |
40.1 to 45 40.1 to 45 |
45.1 to 55 45.1 to 55 |
55 above 55 above |
Body Mass Index Health Problems Required to Qualify |
30 to 34.9 May qualify for Gastric Balloon. This BMI range may also qualify for other procedures if the patient has poorly controlled diabetes or metabolic syndrome. |
35 to 40 May qualify for Gastric Balloon. This BMI range may also qualify for other procedures if the patient has poorly controlled type 2 diabetes, a higher risk of cardiovascular disease, or suffers from another weight-related health issue. |
40.1 to 45 May qualify for any weight loss procedure other than Gastric Balloon. |
45.1 to 55 May qualify for any weight loss procedure other than Gastric Balloon or vBloc Therapy. |
55 above May qualify for any weight loss procedure other than Gastric Balloon, vBloc Therapy, or AspireAssist. |
These qualifications apply for most countries and most procedures, including the U.S., Canada, Australia, and the U.K.
Assuming your BMI qualifies, your next step is to decide which procedures may be a fit for you.
Or you can continue to learn more about body mass index below.
How to Calculate BMI
The BMI Formula and How to Apply It to You
How to Calculate BMI: The BMI Formula and How to Apply It to You
According to the Agency for Healthcare Research and Quality, about 1/3 of all people have the wrong impression of their own body weight (1).
After reading this section, you won’t be one of them!
This section will cover…
How to Calculate BMI Using the BMI Formula
Body mass index is a measure of your weight’s relation to your height. Here’s the BMI formula for pounds/inches and kilograms/meters…
or
BMI (kg/m) = weight / height2
BMI Classifications & How to Interpret Them
Your BMI score can be used to classify your weight status. But don’t take your “classification” too seriously just yet. Moderately overweight people actually live longer than those at “normal” weight (2).
And, by the way, we take issue with the concept of “normal” as determined by classifications like the BMI classifications. So while giving you some idea of where you are with your weight, don’t focus on it too much. Everyone has a different body, and there is not a “one-size-fits-all” body type. These weight classifications (i.e. “healthy weight”) is one example of the many discriminatory challenges the overweight face on a daily basis. More on this can be found on our Obesity Discrimination page.
Here are all the weight classifications for adults and what they mean for bariatric surgery…
Classification* Classification* |
Underweight Underweight |
Healthy Weight Healthy Weight |
Overweight Overweight |
Obesity Class I (“Obese”)
(maybe eligible for bariatric surgery) Obesity Class I (“Obese”)
(maybe eligible for bariatric surgery) |
Obesity Class II (“Severely Obese”)
(maybe eligible for bariatric surgery) Obesity Class II (“Severely Obese”)
(maybe eligible for bariatric surgery) |
Obesity Class III (“Morbidly Obese”)
(maybe eligible for bariatric surgery) Obesity Class III (“Morbidly Obese”)
(maybe eligible for bariatric surgery) |
Obesity Class IV (“Super Obese”)
(maybe eligible for bariatric surgery) Obesity Class IV (“Super Obese”)
(maybe eligible for bariatric surgery) |
Classification Body Mass Index (BMI) |
Underweight Below 18.5 |
Healthy Weight 18.5 – 24.9 |
Overweight 25.0 – 29.9 |
Obesity Class I (“Obese”)
(maybe eligible for bariatric surgery) 30.0 – 34.9 |
Obesity Class II (“Severely Obese”)
(maybe eligible for bariatric surgery) 35.0 – 39.9 |
Obesity Class III (“Morbidly Obese”)
(maybe eligible for bariatric surgery) 40.0 – 49.9 |
Obesity Class IV (“Super Obese”)
(maybe eligible for bariatric surgery) Over 50.0 |
In addition to the questionable names applied to the above classes, the BMI rating system has other limitations…
“Despite its shortcomings, knowing your BMI is a decent first step in determining which health issues you could be at risk for.
It’s also an essential component of getting insurance approval for bariatric surgery.”
- It doesn’t take into account the fact that muscle weighs more than fat, so it overestimates body fat in muscular people and underestimates body fat for people with less muscle mass.
- Fat around the midsection is worse than fat that is evenly dispersed throughout the body. For example, men with a waist circumference over 40 inches and women with a waist circumference over 35 inches have a increased risk of cardiovascular disease compared to people with the same BMI but a smaller waist circumference.
- The same BMI formula is applied to both men and women despite the inherent differences in body fat between them (men’s average BMI is 27.8 while women are at 26.8). For example, women tend to have a slightly higher percentage of body fat and men tend to be slightly heavier relative to their height because of a higher relative muscle mass. Because of this, not having a formula that takes into account gender skews the results, making them less accurate.
Despite its shortcomings, knowing how to calculate your BMI is a decent first step in determining which health issues you could be at risk for. As we’ll get into below, it’s also an essential component of getting insurance approval for bariatric surgery.
In general, you should be concerned about obesity health problems if your BMI is 30 or more or if your BMI is between 25 and 29.9 and you have two or more of the following…
- Cigarette smoking
- Family history of premature heart disease
- High blood glucose (blood sugar)
- High blood pressure (hypertension)
- Low HDL-cholesterol (“good” cholesterol)
- High LDL-cholesterol (“bad” cholesterol)
- High triglycerides
- Physical inactivity (3)
Your doctor will also know how to calculate BMI and will interpret your score along with results from several other tests to diagnose your obesity class and confirm its potential health impacts. If you doubt your BMI score and would like to cross-reference it with another at-home test, see our How to Calculate Body Fat Percentage page.
Why BMI?
Easy to Calculate; Correlated with risks of death and other health conditions
Why BMI?: Easy to Calculate; Correlated with risks of death and other health conditions
In 1998, the National Institutes of Health (NIH) brought together an expert panel who recommended that body mass index be used to determine whether an individual is overweight or obese.
In addition to being a fast, easy, and cheap measurement, the panelists felt that for most people, BMI was a good representation of body fat. They also saw that it directly correlated with the risk of death and several diseases and conditions, including…
- Adult-onset asthma
- Arthritis
- Breathing problems
- Coronary heart disease
- Hypertension
- Ovarian cancer
- Total and ischemic stroke
See our Obesity Health Problems page for a full list of weight-related conditions.
BMI for Children and Teenagers
Different than Adults; Age and Gender Specific
BMI for Children and Teenagers: Different than Adults; Age and Gender Specific
Children and teenagers up to 19 years of age use a different body mass index labeling system than adults (6). They are classified as follows…
Classification Classification |
Healthy Weight Healthy Weight |
Overweight Overweight |
Obesity Class I (“Obese”) Obesity Class I (“Obese”) |
Classification Body Mass Index (BMI) |
Healthy Weight Below the 85th percentile |
Overweight 85th percentile to 94.9th percentile |
Obesity Class I (“Obese”) 95th percentile and above |
In children and teens from 6 to 19 years, BMI is age and gender specific. In other words, a 10 year old male will have a different “normal” BMI than a 15 year old female. Being “overweight” means having a BMI at or above the 95th percentile in their specific age/gender category.
See the CDC’s individual and clinical growth charts to learn where you (or your child) fall.
Also see our Teen Obesity & Adolescent Bariatric Surgery page for more information about obesity in young people and the appropriateness of weight loss surgery for teens.
A Brief History of the Body Mass Index Formula
The 2 Key Innovators
A Brief History of the Body Mass Index Formula: The 2 Key Innovators
Believe it or not, at first body mass index had nothing to do with body fat or health. It had to do with an astronomer’s fascination with statistics.
Two men were the primary drivers of body mass index as a tool…
- Adolphe Quetelet (1796 – 1874), a Belgian astronomer, knew that by repeatedly observing the heavens, statistical laws could be used to predict the movement of the stars. In the 1830’s, he set out to determine whether the same laws could be applied to humans.He proceeded to compile information from various army conscripts, including the weight and height of soldiers. For every height, he found that there was a “bell curve” weight distribution around it. In other words, at each height there was an average weight range that was most common. The lighter or heavier a person was compared to the average weight range, the less common their weight.He concluded that the top of the bell curve constituted a “normal” weight and that anyone who deviated from it was over- or under-weight (5).
- Louis Dublin (1882 – 1969), a statistician at the Metropolitan Life Insurance Company, is largely responsible for the use of body mass index as a health indicator. He was familiar with the concepts that Quetelet discovered, and he wanted to find a better way to determine the risk of his company’s life insurance clients and found that…
- Thinner people lived longer, and
- The closer one’s weight to the average 25 year old, the longer they lived. He then determined the weight range at which a person should live the longest (6).
-
Doctors and the government quickly took his lead and began using his findings to determine who was considered “overweight” and how weight status could further be used as a predictor of health risks.
