How "ideal weight" formulas actually work
Ideal body weight formulas were originally developed for clinical purposes — most commonly, calculating safe drug dosages, where using actual body weight for someone with a very high or low BMI could lead to over- or under-dosing. The Devine formula, used here, is one of the most established:
Men: IBW(kg) = 50 + 2.3 × (height in inches − 60)
Women: IBW(kg) = 45.5 + 2.3 × (height in inches − 60)
Like BMI, it only takes height as an input, which means it can't account for frame size, muscle mass, or individual body composition. Two people of the same height with very different builds will get the same "ideal weight" from this formula, even though their genuinely healthy weights might differ by 10kg or more.
How to use this number sensibly
Treat the result as a rough reference point, not a target to hit precisely. The ±10% range shown alongside the main number reflects the genuine variation in healthy weight at a given height — if your actual weight sits within or close to that range and you feel well, energetic, and capable, the exact number matters far less than those broader signals of health.