About Health Calculator
These are the numbers people look up most often, and they are worth getting right — along with being clear about what each one actually measures. Every formula here is a population-level estimate fitted to a study group. An individual can sit a long way from the average with nothing at all being wrong.
Where more than one formula is in common use, the modern one is used and the older shown alongside. Resting energy is calculated with Mifflin–St Jeor, which predicts measured values more accurately than Harris–Benedict and is why dietitians moved to it — but Harris–Benedict is displayed too, because many calculators still use it and produce a different number for the same person. Seeing both is more useful than wondering which is wrong.
Ideal weight is deliberately shown as four answers rather than one. Devine, Robinson, Miller and Hamwi disagree by several kilograms for the same height, and presenting a single figure would imply a precision that does not exist.
Nothing you enter is transmitted. Height, weight, age and body measurements are personal, and there is no reason for a calculator to see them — everything happens in this browser tab.
How to use the calculators
Pick metric or imperial
Switching converts the values you have already entered rather than reinterpreting the numbers.
Enter your details
Weight, height, age and sex drive every tab. Results update as you type.
Choose a calculation
BMI, calorie needs, body fat or ideal weight. Each explains the formula it uses.
Read the caveats
Each result comes with what it cannot tell you, which is often the more useful half.
What each number actually measures
- BMI — weight against height. It knows nothing about body composition, which is why muscular people are routinely classed overweight.
- BMR — energy your body uses at complete rest, before any movement at all.
- TDEE — BMR multiplied by an activity factor. The factor is the least precise part; if your weight is stable, your real intake is a better estimate of maintenance than any formula.
- Body fat — estimated from circumferences, typically within three or four percentage points of a DEXA scan.
- Ideal weight — four formulas from the 1970s and 80s, none of which account for build.
Why calculators disagree with each other
Different sites use different formulas without saying which. A BMR from Harris–Benedict and one from Mifflin–St Jeor can differ by over a hundred calories for the same person, and neither is wrong — they are different models fitted to different data.
Activity multipliers vary even more. The factors used here are the widely published ones, but the gap between sedentary and lightly active is a judgement call that no formula can make for you. The practical approach is to pick a number, eat to it for a few weeks, and adjust based on what the scale actually does.