Ideal weight

There is no one ideal weight. What formulas spit out are averages for the population – your healthy weight is a range in which you feel fit, comfortably full and able to move freely, and your blood test results are where they should be. Even so, the formulas are useful for finding a realistic goal.

The oldest is the Broca formula, devised by the French physician Paul Broca (1871): height in centimetres minus 100 gives the “normal weight” in kilograms – so 70 kg at 170 cm. To get the “ideal weight”, 10% (men) or 15% (women) was later subtracted – which is now considered too strict. More widely used is the BMI range of 18.5 to 24.9: at 170 cm, that corresponds to 53 to 72 kg – a span of almost 20 kilos with room for lots of different bodies. The Devine formula (1974) starts from 50 kg (men) or 45.5 kg (women) and adds 2.3 kg for every 2.54 cm above 152 cm.

Which weight within this range suits you depends on your build, muscle mass, age and genetic make-up. Some people feel good at a BMI of 21, others at 24 – both are healthy. What matters more than the number is where the fat sits: a waist measurement of less than half your height is more protective than a “perfect” BMI.

For weight-loss goals, professional bodies recommend small steps: losing just 5 to 10% of your weight noticeably improves blood pressure, blood sugar and blood fats – at 90 kg, that's 4.5 to 9 kg. A “feel-good weight” that you can maintain without constant hunger beats any theoretical ideal weight that's gone again after three months.

For children and teenagers, there is no ideal weight in kilos – their weight is assessed using percentiles for age and height. And anyone below the normal range doesn't have a weight-loss goal; instead, they may need medical advice.