Carolyn Nicholls, now 47, from Nottingham. BMI, or body mass index, is your weight (in kilograms) divided by the square of your height (in metres). An ideal BMI is in the 18.5 to 24.9 range for most adults, according to the NHS. However, even the NHS acknowledges that it “is not the perfect measure of your overall health,” noting that BMI “can’t tell if you’re carrying too much fat or you’ve got a lot of muscle.” In a recent House of Lords debate on BMI, former Olympic silver medallist Sir Colin Moynihan pointed out that many Olympic athletes would be considered above the “healthy” BMI measure. Meanwhile, some patients have been denied access to eating disorder services if their BMI is not considered “low enough”.