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For adults (18+). Weight is optional — add it to also see your BMI and daily calories.
Last updated 3 September 2026
Why height matters more than age
A healthy weight is a function of how tall someone is, not how many birthdays they've had. Two adults the same age can have completely different healthy weights if their heights differ, and two adults the same height can be the same age or forty years apart and still share roughly the same healthy range. That's why this calculator asks for height and sex first — age only comes into the calorie and metabolic-rate estimates further down, where it genuinely changes the number.
How the numbers are calculated
- Healthy range — the weights at which your BMI would sit at 18.5 and at 24.9, the standard boundaries of the "healthy weight" band.
- Ideal weight — a single figure from the Devine formula, a reference equation from clinical medicine that has been used to guide medication dosing for decades.
- BMI — your current weight divided by height squared, shown only if you entered a current weight.
- BMR — calories your body burns at complete rest, estimated with the Mifflin-St Jeor equation. An Academy of Nutrition and Dietetics evidence review found it lands within 10% of measured values more often than the other equations in common clinical use, though individual error can be larger.
- Daily calories — your BMR multiplied by an activity factor, giving a rough calorie target for maintaining your current weight.
Method, limitations and sources
Formulas. The healthy weight range comes from the Devine formula (1974), extended below five feet of height. BMI is weight in kilograms divided by height in metres squared. BMR uses the Mifflin-St Jeor equation, and daily calories multiply that by an activity factor.
Inputs it needs. Height, and for the BMI and calorie figures also weight, age, sex and activity level.
What it assumes. That a single height-based figure is meaningful for an adult. The Devine formula was originally devised for calculating medication doses, not for setting personal weight goals, and it takes no account of build, muscle mass or frame size. Two healthy adults of the same height can sit several kilograms apart.
Where it is least reliable. Muscular or athletic people, older adults who have lost muscle, anyone very short or very tall, pregnant women, and children and teenagers — for whom BMI must be read against age-and-sex growth charts, not adult cut-offs. BMI cannot distinguish fat from muscle or bone, and does not show where fat is carried.
When not to use it. Do not treat the range as a target you must hit, and do not use it to justify a restrictive diet. A weight outside the range is a prompt for a conversation with a doctor, not a verdict.
- CDC — About Body Mass Index, including what BMI does and does not measure.
- Devine BJ. Gentamicin therapy. Drug Intelligence and Clinical Pharmacy, 1974;8:650–655 — the origin of the ideal body weight formula.
- Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241–247.
Common questions
Why does this need my height, not just my age?
A healthy weight depends on how tall you are, not how old you are. Two 30-year-olds of different heights have different healthy weights. Age matters only for the calorie and metabolic-rate estimates, not for the weight range itself.
Why adults only?
Under 18, healthy weight is judged against age-and-sex growth charts and percentiles, not a fixed adult formula. That is a different calculation that needs paediatric reference data, so this tool sticks to ages 18 and up where it can be accurate.
Where do the healthy range and ideal weight numbers come from?
The range comes from the standard BMI band of 18.5 to 24.9 applied to your height. The single ideal-weight figure uses the Devine formula, a long-standing reference formula from clinical medicine. Both are estimates, not a verdict on any individual body.
Is this medical advice?
No. It is a general reference calculation. Muscle mass, bone density, pregnancy and many health conditions all affect what a healthy weight looks like for a given person, so treat this as a starting point and talk to a doctor for anything personal.
Is my data saved anywhere?
No. Everything is calculated in your browser and nothing is sent anywhere or stored.