What is BMI

The body mass index, or BMI, is a metric used to estimate the amount of body fat a person has. It’s a measure of relative weight based on an adult's mass and height.

Body mass index is one method used to estimate your total body fat. This helps to determine if your weight is within the normal range, or if you are underweight or overweight.

What is BMI

Differences in BMI between people of the same age and sex are usually due to body fat.

But BMI does not differentiate between body fat and muscle mass, which means a BMI figure may not be accurate.

BMI calculations will overestimate the amount of body fat for:

  • Body builders.
  • High-performance athletes.
  • Pregnant women.

BMI calculations will underestimate the amount of body fat for people with a physical disability, who are unable to walk and may have muscle wasting, and for the elderly. For people with eating disorders like anorexia nervosa, BMI is also not an accurate indicator.

To learn more about the limitations of BMI calculations and its accuracy in assessing body composition, explore our comprehensive guide here.

What is my BMI

BMI is an approximate measure of the best weight for health only.

To calculate your BMI, you can use our Best BMI calculator. You need to know your weight and height.

Once you have calculated your BMI, you can determine your healthy weight range:

15 and below Very Severely Underweight
15 – 15.9 Severely Underweight
16 – 18.4 Underweight
18.5 – 24.9 Healthy weight
25 – 29.9 Overweight
30 – 34.9 Moderately obese
35 – 39.9 Severely obese
40 and above Very Severely obese (morbid obesity)

For most adults, an ideal BMI is in the 18.5 - 24.9 range.

If your BMI is less than 18.5, you weigh less than is ideal for your height, and if your BMI is 25 or more, you weigh more than is ideal for your height.
Use ideal-weight.net to determine your ideal body weight. This ideal weight calculator can help you determine if you should be considering a diet.

BMI can also be determined using from a chart which displays BMI as a function of mass and height using contour lines, or colors for different BMI categories, and may use two different units of measurement

Overweight BMI

Overweight is having more body fat than is optimally healthy. If your BMI is 25 or more, you should think about losing weight. Being overweight (or obese) can increase your risk of health problems, such as:

  • Heart disease,
  • stroke,
  • type 2 diabetes,
  • Oligospermia (in men),
  • some types of cancer (colon / breast cancer),
  • high blood pressure (hypertension),
  • Depression,
  • Gallbladder disease.

Obesity is most commonly caused by a combination of excessive food energy intake, lack of physical activity, and genetic susceptibility, although a few cases are caused primarily by genes, endocrine disorders, medications, or psychiatric illness. As a result, obesity has been found to reduce life expectancy. Obesity is one of the leading preventable causes of death worldwide.

Underweight BMI

If your BMI is less than 18.5, you may want to talk to your doctor about gaining weight. A person may be underweight due to metabolism, lack of food, genetics or illness. Being underweight can also increase your risk of health problems, such as:

  • Osteoporosis (brittle bones),
  • Amenorrhea (absent periods in women),
  • Anemia (iron deficiency),
  • Hyperthyroidism,
  • Digestive diseases,
  • Respiratory disease,
  • Tuberculosis,
  • And some types of cancer.

Low body mass can decrease your body's immune system, which could lead to illness such as malnutrition, bone loss, and other conditions. The lower your BMI the greater these risks become.

The risk of death increases by 20 to 40 percent among overweight people.