# BMI Calculator Inaccurate, Says Oxford Professor

Published January 22, 2013

If you’ve been relying on your BMI to determine if you’re overweight, it may be time to get a second opinion.

Professors at Oxford University have found the mathematical equation used to calculate body mass index (BMI) is inaccurate.

The academics argue the current equation does not take into account that a person’s weight tends to grow with their height.

“BMI divides the weight by too large a number for short people and too small a number for tall people,” Nick Trefethen, a leading mathematician at the prestigious university, told Business Insider.

"So short people are misled into thinking that they are thinner than they are, and tall people are misled into thinking they are fatter.”

To correct this issue, Trefethen has developed a new formula to correctly calculate BMI.

The use of the BMI is common by doctors to determine if a person is overweight or obese.

Traditionally a BMI between 18.5 and 24.9 is normal, while less than 18.5 is seen as underweight and 25 to 29.9 is considered overweight. A  BMI of 30 or above means a person is obese.

Trefethen discovered the issue with the way the BMI is measured after the conventional calculation methods failed to take into account that taller people tended to be bulkier than those who were shorter.

Belgian scientist Adolphe Quetelet, who developed the index in the 1830s, recognized the potential flaws early on.

“We know that BMI is a good indicator of population level trends, but not always a good indicator at an individual level."

Trefethen has linked to the new calculator on his website to let people see if the new calculations effect their BMI.