Ideal weight calculators estimate a healthy target body weight based primarily on height and sex, using formulas developed decades ago, originally for medical dosing purposes (calculating drug dosages based on an estimated 'ideal' rather than actual body weight). Several formulas exist — including Devine, Robinson, Miller, and Hamwi — each giving a slightly different result, since they were derived from different population datasets.

It's important to understand that 'ideal weight' from these formulas is a rough population-level estimate, not a personalized target. They don't account for individual differences in muscle mass, bone density, body frame size, or body composition — two people of the same height and sex can have very different healthy weights depending on their build.

Because of these limitations, most healthcare providers consider ideal weight formulas a starting reference point at best, often used alongside BMI, body fat percentage, and overall health assessment rather than as a standalone target to hit.