Calorie calculator
Resting rate, daily energy, and how rough both of them are.
“Formula variant” is exactly that — Mifflin-St Jeor was fitted with two constants and this picks between them. It is not a question about you.
- To maintain your weight2,556 kcal
- Resting metabolic rate1,649 kcal
- 500 kcal deficit a day2,056 kcal
- 500 kcal surplus a day3,056 kcal
Rounded to four figures, which already overstates it — the underlying estimate is good to roughly ±10% for a group and less for any one person.
Two estimates stacked on each other
The resting figure comes from Mifflin-St Jeor, a regression fitted to a few hundred adults in 1990. It predicts a group average to about ±10% and any individual rather worse — real resting rates vary with body composition, thyroid function, genetics and things nobody has put in a formula. It replaced Harris-Benedict, which ran about 5% high; if another calculator disagrees with this one by roughly that, that is usually why.
The daily figure then multiplies that estimate by an activity factor picked from five buckets. The gaps between those buckets are wider than most people’s ability to place themselves in one, so choosing “moderate” instead of “light” moves the answer by more than the underlying formula’s error. That is the larger uncertainty, and it is a choice made by the person filling in the form.
Which is the honest summary: treat the output as a starting bracket to compare against what actually happens over a few weeks, not as a target to hit.
About the 500 kcal rows
Those are subtraction and addition, and nothing more. The familiar rule that 500 kcal a day is about half a kilogram a week rests on treating body fat as roughly 7,700 kcal per kilogram — an average of an average — and it assumes the body does not adjust, which over weeks it does. They are shown because people ask for them, labelled as arithmetic because that is what they are.
This page cannot know your health, your history or your medication, and it is not a substitute for someone who can. If you are making decisions about how much you eat — particularly if you are unwell, pregnant, an athlete, or have any history of disordered eating — that belongs with a doctor or a registered dietitian rather than with a static web page doing multiplication.
