Daily energy calculator
Fill in the day you usually have, not the day you wish you had. The result above updates as you type and is computed in your browser; nothing leaves the page.
What the number means
The calculator estimates your total daily energy expenditure — everything your body spends in a day — in three layers, the same three the step on daily energy walks through:
- Resting energy from the Mifflin–St Jeor equation, using sex, age, height and weight.
- Your ordinary day, hour by hour: sleep, work of a given heaviness, the commute and the rest of the waking day, each weighted by a physical-activity ratio. A day off is modelled separately, because for most people it is not a work day with the work removed.
- Deliberate exercise from the MET value of the activity, its duration and your weight, minus the ordinary hour it displaces, with a small allowance for the afterburn and a credit of 85 percent so that a planned session that turns out lighter than planned does not overstate the day.
The headline is a range of plus or minus ten percent around the weekly average. That is not caution for its own sake: the resting-energy equation alone is off by ten percent or more for a sizeable minority of people, and each further layer adds its own error. Two calculators that disagree by two hundred calories are both within the model.
What to do with it
Use the average as a starting point, eat to a target below it for two or three weeks while logging honestly, and let the trend of the scale correct the estimate. The realistic pace step explains how large a deficit is worth aiming for and why the answer depends on your weight.
Where the numbers come from
The physical-activity ratios follow the FAO/WHO/UNU human energy requirements report; the MET values are from the 2024 Compendium of Physical Activities; the resting-energy equation is Mifflin and colleagues' 1990 one, chosen because a later systematic review found it the most reliable of the common equations in adults. The exact constants are the ones the app uses, and a test in the app's build compares this page's calculation with the app's for fixed inputs, so the two cannot drift apart unnoticed.
In the app
The app runs the same model from the day you actually had — the sleep you logged, the sessions you planned or did — rather than from a typical one, and re-issues the daily target when the day changes. This page cannot do that; it can only show you the typical day and the size of the error around it.