BMR and daily calorie calculator
Basal metabolic rate and your daily total, from all three published equations — with the error bar the researchers published, because it is six times wider than the disagreement everybody argues about. Nothing you type here leaves your browser — it is worked out on your own device, so there is nothing to send and nothing to log.
The argument everybody has is the smaller half
Search for a BMR calculator and you will find arguments about which equation to use. Harris-Benedict or Mifflin-St Jeor, 1919 or 1990, original or revised.
Measured, for one person: the three equations differ by about 70 kcal. One equation’s own published 95% range is 426 kcal wide.
So the thing that gets argued about moves your answer by a sixth of what your own individual variation does. Picking the right formula is worth having; it is not worth the attention it gets, and no amount of choosing well makes the band narrow.
And the recommended one is right about half the time
Frankenfield’s systematic review for the American Dietetic Association compared the equations against measured resting metabolic rate. Mifflin-St Jeor landed within 10% for 50.4% of people. Harris-Benedict managed 36.8%.
Mifflin-St Jeor is the equation the Academy of Nutrition and Dietetics recommends when resting metabolic rate cannot be measured, and it is the best available. It is also, on those numbers, a coin toss.
That is not a reason to ignore it. It is a reason to treat the output as a starting point that wants adjusting against what actually happens, rather than a figure to plan around.
The default is a hundred years old
Harris and Benedict published in 1919. Roza and Shizgal refitted the coefficients in 1984 on 337 people. Mifflin-St Jeor came in 1990 from 498 people aged 19 to 78, and performs better.
Most calculators still default to Harris-Benedict, usually the original. This page gives all three, says which is recommended, and shows how often each one actually lands.
The activity multipliers are conventions
1.2 for sedentary through 1.9 for very active. They are quoted identically across the literature, no source gives them an error bar, and they are the least examined part of the whole calculation.
Multiplying an estimate that is right half the time by a number chosen from a list of five does not make it more precise — it scales the error bar along with the answer. A ±213 kcal band at rest becomes ±330 at a moderate multiplier, and this page carries it through rather than dropping it.
What this is not
It is not a diet plan, and there is no deficit calculator here. It does not know your body composition, your thyroid, your medication, how much you sleep or how much you fidget — and fidgeting alone accounts for a surprising share of the variation between two people of the same size.
Katch-McArdle, which uses lean body mass instead of height and age, is not shown beside these: it answers a different question from different inputs, and lining it up with the others as though they were interchangeable would be the mistake this page is about.
Where these come from
Harris, J. A., & Benedict, F. G. (1919). · Roza, A. M., & Shizgal, H. M. (1984). “The Harris Benedict equation reevaluated.” · Mifflin, M. D., St Jeor, S. T., et al. (1990). · Frankenfield, D., Roth-Yousey, L., & Compher, C. (2005). “Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review.” Journal of the American Dietetic Association 105(5): 775–789.