Body Mass Index (BMI) Calculator

Enter your current weight (kilograms or pounds) and your height (feet and inches, or just inches, or centimetres), then press Calculate. That gives your basic Body Mass Index. Then add your age and gender to see how you compare with others in the general population of the same age and sex.

What does it all mean?

You now have both your Body Mass Index and your weight percentile. The calculator also gives you a body description, which falls into one of five categories: Underweight, Within Normal Range, Marginally Overweight, Overweight, or Obese. You can switch those definitions between the World Health Organization and Centers for Disease Control (WHO / CDC) values and Dr. Halls' own age-and-gender-adjusted values using the setting above.

It is important to remember that, with the halls.md calculations, your Body Mass Index threshold changes with both your age and your gender. A given BMI can mean something different for a teenager, an adult woman and an adult man.

Underweight

If your body description is underweight (usually taken as a BMI below 18.5), there are a few things to consider. You know yourself best: if you feel and look healthy, that counts for a lot. But if you have rapid weight loss, or are gradually losing weight without trying, it is worth seeing your physician to rule out a medical cause. Conditions that can contribute to a low BMI include an overactive thyroid, digestive problems such as Crohn's disease or irritable bowel syndrome, some cancers, and depression or anxiety. One of the main concerns of being underweight is that you may also be malnourished, though you can be overweight and malnourished at the same time.

Within normal range

If your BMI falls within the normal range, that is good news. It does not settle everything, though. Body Mass Index on its own says nothing about body composition, which is the ratio of muscle to body fat, known as your body fat percentage. Two people of the same height and weight can carry very different amounts of fat and muscle. Only you know best how you feel about your own body weight.

Marginally overweight

Falling into this group is not bad news. It is best seen as a warning to adopt a few healthy habits. If you are a body builder, an athlete, or have a muscular build, you may land in this group simply because muscle is dense, and the BMI itself does not tell the difference. For everyone else who has put on a few pounds and is not happy about it, it is a good moment to look at diet and activity before the numbers move further.

Overweight and Obese

The categories of overweight and obese are controversial within medicine, and it is worth remembering that they are only categories. On this calculator the obese range begins above 32.2 for women and above 31.1 for men. The halls.md overweight threshold sits at about 27.3 for women and 27.8 for men, which is higher than the simpler WHO and CDC cut-offs of 25 and 30. However you classify it, if you are overweight or obese, losing even a few pounds can make a real difference to your health.

Being overweight or obese raises the chances of high blood pressure, heart attack and stroke, arthritis, diabetes, respiratory problems, gout, gallbladder disease and gallstones, and some cancers. That list is not meant to frighten anyone; it is meant to motivate. Every new day is a new chance to change your life.

Why is waist circumference important?

Belly fat is an important indicator of general health. In general, a large waist circumference, regardless of your BMI, is linked with a higher risk of cardiovascular disease, diabetes, Alzheimer's disease, and some cancers, particularly colon, prostate and breast cancer. Your waist measurement has health implications whether or not your BMI is in the normal range, and this is a neat illustration of how a normal BMI can still come with a higher risk if body fat is distributed around the middle.

Why calculate your Body Mass Index?

The body mass index was developed as a screening tool for medical professionals to assess the general weight categories of their patients. For everyone else it is a guide, and the operative word is guide. There are many other factors besides height and weight that point to a healthy body: the quality of your diet, your level of physical activity, your body fat percentage, your waist measurement, and any obesity-related health problems. If your BMI score does not reflect your actual body type, do not take too much notice of it.

A last word on this calculator

This is the Body Mass Index and weight percentile calculator that began on halls.md in 1999, and it has been adjusted over the years as the research changed. It was ahead of its time in two ways: it was the first to take your age and your gender into account, and the weight percentile feature lets you compare yourself with others in the population of the same age and sex. In 1999 it was the first BMI calculator to say that healthy weight changes with age, and that a single set of overweight and obesity thresholds was too simplistic. Because it stayed at number one for many years, millions of people used it, and this age-and-gender approach has since become generally accepted in medicine.

The Talking Moose, mascot since 1999.

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Supporting pages on the evidence behind these numbers are being restored and will be linked here.