Ideal Weight vs. Healthy Weight: Which Target Should You Use?

Search for what you should weigh and you will find two kinds of answer. One gives you a single number and calls it your ideal body weight. The other gives you a range and calls it your healthy weight. They come from completely different places, and the difference matters more than the similar names suggest.

Ideal body weight formulas were built for medicine — specifically, for working out drug doses. Healthy weight ranges come from epidemiology: large studies of what body weights are associated with the lowest rates of death and disease. Only the second was ever intended as guidance about what to weigh.

In 1974 B.J. Devine published a formula for estimating ideal body weight in a clinical pharmacy journal. The purpose was practical: some drugs distribute through lean tissue rather than fat, so dosing a very heavy patient by total body weight can produce a dangerous overdose. Devine needed a quick way to estimate the lean-tissue-relevant weight for a given height.

The formula was published without derivation and without supporting data. It was a rule of thumb, and it worked well enough for its purpose. Robinson, Miller and Hamwi followed over the next decade with their own variants, each fitted slightly differently. A later review traced all of them back to mid-twentieth-century life insurance height-weight tables — data drawn from policyholders, which is not a representative sample of anything.

None of these was ever validated against health outcomes. They are estimates of a typical weight for a height, made for a clinical task that required speed rather than precision.

Every ideal body weight formula has the same structure: a base weight at five feet, plus a fixed increment per additional inch. The imperial anchoring is a giveaway about their origins.

That linear form is where they run into trouble. Human bodies do not scale linearly with height, so the four formulas agree reasonably in the middle of the range and diverge at the extremes. At 5'10", the four give answers spanning about five kilograms. At 6'4" the spread is wider still.

This is why this site shows all four rather than picking one. A single confident number implies a precision that does not exist, and the disagreement between four equally published formulas is the most honest information available about how much to trust any of them.

There is a second, quieter problem with the linear form. Because every formula adds a fixed weight per inch regardless of build, it implicitly assumes that everyone of a given height should have the same frame. Two people at 5'8" with visibly different bone structure — different shoulder width, different wrist and ankle circumference — receive the same target. Frame size is real, measurable and entirely absent from these equations, which is one reason the numbers often strike broader-framed people as absurdly low.

The healthy weight range is the WHO's normal BMI band — 18.5 to 25 kg/m² — rearranged to give weight for a given height. The band itself comes from outcome data rather than from a rule of thumb.

The largest analysis of that relationship pooled 239 prospective studies covering roughly ten million people and found mortality lowest in a broad, flat trough between about 20 and 25 kg/m², rising steadily above it. The word to hold onto there is 'trough'. It is not a sharp minimum with one correct value; it is a wide, shallow basin in which the data does not meaningfully distinguish one weight from another.

That shape is why a range is the honest output. At 175 cm the band spans roughly 57 to 77 kilograms — a twenty-kilogram window that comfortably holds bodies which look very different from one another and are all, by this measure, fine.

For nearly everyone reading this, the answer is the range. It is derived from health outcomes rather than dosing convenience, it is wide enough to be achievable, and it does not imply a false precision.

The ideal weight formulas remain exactly right for their intended purpose. If you are a clinician sizing a dose of a lean-tissue-distributed drug, or setting tidal volumes on a ventilator, Devine's formula is the correct tool and this is not a criticism of it.

There is a third answer that beats both, and it is the one most likely to actually happen: aim for the next five per cent.

Most of the measurable health benefit of weight loss arrives early. Trials in overweight and obese adults have repeatedly found that a 5 to 10 per cent reduction produces clinically meaningful improvements in blood pressure, triglycerides, HDL cholesterol and glycaemic control. Further loss adds progressively less.

For someone at 100 kilograms, that is five to ten kilograms — a target that is reachable in a few months and holdable afterwards. Compare it with a BMI table implying thirty, which is achievable for some people and abandoned by most. A goal you reach and keep is worth more than a goal that is technically optimal and statistically abandoned.

Neither the ideal weight number nor the healthy weight range is an entry requirement. Both are directions of travel, and the first stretch of the journey is where nearly all the benefit is.

It is also worth knowing in advance that holding a reduced weight is physiologically distinct from reaching it. Appetite hormones shift after weight loss and the changes persist — one well-known study found ghrelin still elevated and satiety hormones still suppressed a full year after a supervised diet. The pull back toward the old weight is real and it is not a failure of willpower. People who expect it, and who build their eating around something they could continue indefinitely rather than something they endure temporarily, do considerably better than people who treat the target as a finish line.