The easiest way to find out if you should be concerned about your weight is to determine your Body Mass Index or BMI. It is a number, usually between 16 and 40 that is calculated from your height and weight. The higher your BMI, the greater your risk.

The BMI categories are: Healthy Weight, Moderately Overweight and Severely Overweight. These categories are based on the government's 1998 Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults.  Please note this calculator is meant for adults, male or female, who are not frail, elderly, pregnant, nursing, extreme body building, or disabled.

Calculate Your Body Mass Index

• What is BMI?
• How is BMI used?
• Why does CDC use BMI to measure overweight and obesity?
• What are some of the other ways to measure obesity? Why doesn’t CDC use those to determine overweight and obesity among the general public?
• How is BMI calculated and interpreted?
• How reliable is BMI as an indicator of body fatness?
• If an athlete or other person with a lot of muscle has a BMI over 25, is that person still considered to be overweight?
• What are the health consequences of overweight and obesity for adults?
• Is BMI interpreted the same way for children and teens as it is for adults?

What is BMI?

Body Mass Index (BMI) is a number calculated from a person’s weight and height. BMI is a reliable indicator of body fatness for people. BMI does not measure body fat directly, but research has shown that BMI correlates to direct measures of body fat, such as underwater weighing and dual energy x-ray absorptiometry (DXA).1, 2 BMI can be considered an alternative for direct measures of body fat. Additionally, BMI is an inexpensive and easy-to-perform method of screening for weight categories that may lead to health problems.

How is BMI used?

BMI is used as a screening tool to identify possible weight problems for adults. However, BMI is not a diagnostic tool. For example, a person may have a high BMI. However, to determine if excess weight is a health risk, a healthcare provider would need to perform further assessments. These assessments might include skin fold thickness measurements, evaluations of diet, physical activity, family history, and other appropriate health screenings.

What are some of the other ways to measure obesity?

Other methods to measure body fatness include skin fold thickness measurements (with calipers), underwater weighing, bioelectrical impedance, dual-energy x-ray absorptiometry (DXA), and computerized tomography. However, these methods are not always readily available, and they are either expensive or need highly trained personnel.

How is BMI interpreted?

Interpretation of BMI for adults
For adults 20 years old and older, BMI is interpreted using standard weight status categories that are the same for all ages and for both men and women. For children and teens, on the other hand, the interpretation of BMI is both age- and sex-specific. For more information about interpretation for children and teens, visit Child and Teen BMI Calculator.

The standard weight status categories associated with BMI ranges for adults are shown in the following table.

For example, here are the weight ranges, the corresponding BMI ranges, and the weight status categories for a sample height.

How reliable is BMI as an indicator of body fatness?

The correlation between the BMI number and body fatness is fairly strong; however the correlation varies by sex, race, and age. These variations include the following examples: 3, 4

• At the same BMI, women tend to have more body fat than men.
• At the same BMI, older people, on average, tend to have more body fat than younger adults.
• Highly trained athletes may have a high BMI because of increased muscularity rather than increased body fatness.

It is also important to remember that BMI is only one factor related to risk for disease. For assessing someone’s likelihood of developing overweight- or obesity-related diseases, the National Heart, Lung, and Blood Institute guidelines recommend looking at two other predictors:

• The individual’s waist circumference (because abdominal fat is a predictor of risk for obesity-related diseases).
• Other risk factors the individual has for diseases and conditions associated with obesity (for example, high blood pressure or physical inactivity).

For more information about the assessment of health risk for developing overweight- and obesity-related diseases, visit the following Web pages from the National Heart, Lung, and Blood Institute:

• Assessing Your Risk
• Body Mass Index Table
• Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults

If an athlete or other person with a lot of muscle has a BMI over 25, is that person still considered to be overweight?

According to the BMI weight status categories, anyone with a BMI over 25 would be classified as overweight and anyone with a BMI over 30 would be classified as obese.

It is important to remember, however, that BMI is not a direct measure of body fatness and that BMI is calculated from an individual’s weight which includes both muscle and fat. As a result, some individuals may have a high BMI but not have a high percentage of body fat. For example, highly trained athletes may have a high BMI because of increased muscularity rather than increased body fatness. Although some people with a BMI in the overweight range (from 25.0 to 29.9) may not have excess body fatness, most people with a BMI in the obese range (equal to or greater than 30) will have increased levels of body fatness.

It is also important to remember that weight is only one factor related to risk for disease. If you have questions or concerns about the appropriateness of your weight, you should discuss them with your healthcare provider.

What are the health consequences of overweight and obesity for adults?

The BMI ranges are based on the relationship between body weight and disease and death.5 Overweight and obese individuals are at increased risk for many diseases and health conditions, including the following: 6

• Hypertension
• Dyslipidemia (for example, high LDL cholesterol, low HDL cholesterol, or high levels of triglycerides)
• Type 2 diabetes
• Coronary heart disease
• Stroke
• Gallbladder disease
• Osteoarthritis
• Sleep apnea and respiratory problems
• Some cancers (endometrial, breast, and colon)

Is BMI interpreted the same way for children and teens as it is for adults?

Although the BMI number is calculated the same way for children and adults, the criteria used to interpret the meaning of the BMI number for children and teens are different from those used for adults. For children and teens, BMI age- and sex-specific percentiles are used for two reasons:

• The amount of body fat changes with age.
• The amount of body fat differs between girls and boys.

Because of these factors, the interpretation of BMI is both age- and sex-specific for children and teens.

For adults, on the other hand, BMI is interpreted through categories that are not dependent on sex or age

*some information has been taken from the CDC website

If your BMI indicates that you are either Moderately Over Weight or Severely Over Weight, you need to start and maintain a healthy lifestyle.

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