BMI Calculator, With the Honest Caveats

For most adults, a BMI between 18.5 and 24.9 is considered the healthy range. From 25 to 29.9 counts as overweight, and 30 or above counts as obese. BMI is a screening number, not a diagnosis, so use it as a starting point for a conversation with your own doctor.

BMI only compares weight to height, so it cannot tell muscle from fat. A muscular person can score as overweight while carrying very little fat, and an older person can have a normal BMI while having lost muscle and gained fat around the middle. That is why doctors often look at waist size and overall health alongside BMI.

Research shows that people of Asian background tend to develop diabetes and heart disease at lower BMI levels than others. Because of this, many health bodies use a cut-off of 23 for overweight and 27.5 for obesity in Asian adults instead of 25 and 30. If this applies to you, the standard chart may understate your risk, so discuss it with your doctor.

For predicting health problems, waist size is often the more useful number, because fat stored around the organs in your belly is the kind most linked to diabetes and heart disease. A common rule of thumb is to keep your waist under half your height. A large waist with a normal BMI is still worth raising with your doctor.