Calorie Calculator

Harris–Benedict, developed in 1919, was for decades the standard equation for estimating basal metabolic rate, but it was derived from a study population that does not resemble a modern, more sedentary population particularly well, and subsequent validation studies have repeatedly found it tends to overestimate BMR for a meaningful share of people today. Mifflin–St Jeor, published in 1990 from a larger and more contemporary dataset, has consistently been found more accurate against measured energy expenditure in the decades of validation research since, which is why current nutrition and dietetics guidance generally recommends it as the better default equation — not because Harris–Benedict was wrong for the population it was built from, but because it does not generalise as well to people today.

Basal metabolic rate — the energy the body burns at complete rest — is a relatively stable number for a given age, sex, height and weight, and BMR calculations tend to be reasonably consistent between formulas. The activity multiplier applied on top of that BMR to estimate total daily expenditure ranges from around 1.2 for a sedentary lifestyle to roughly 1.9 for very intense physical activity, and choosing the wrong multiplier moves the final estimate by a far larger margin than any difference between BMR formulas ever could. This also happens to be the input people get wrong most often and most consistently, and in a predictable direction: it is extremely common to round a few weekly gym visits up to "very active" when the honest classification for most such routines is closer to "lightly" or "moderately" active — an overestimate at exactly the step that has the largest leverage on the final number.

The conventional figure that a 500-calorie daily deficit produces roughly a pound of fat loss per week comes from a widely cited approximation that a pound of body fat represents about 3,500 stored calories — a genuinely useful rule of thumb, but not a precise, predictable formula that applies with the same regularity to every individual, and more recent metabolic research has shown the real relationship is more complicated than a fixed constant, particularly as a person continues losing weight and their metabolism adapts to the new lower body weight. Day-to-day scale weight also fluctuates substantially due to water retention, sodium intake, hormonal cycles and digestive contents — swings that can easily mask or exaggerate several days of genuine fat loss or gain. Judging progress by a rolling average across several weeks, rather than any single morning's scale reading, is what actually reflects the underlying trend the calorie math is describing.