Calorie calculator

How this is calculated

Your resting energy expenditure comes from the Mifflin St Jeor equation, published in the American Journal of Clinical Nutrition in 1990 and still the general-population default. It estimates the energy your body uses at complete rest.

BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + s
where s = +5 for men and −161 for women

That figure is then multiplied by an activity factor to give maintenance calories, rounded to the nearest 10 because the underlying estimate is nowhere near single-calorie precision. Finally a deficit or surplus is applied for your goal.

This is the same arithmetic the Phasebuilt plan generator runs, not a separate implementation. A plan built from the same inputs will show the same number.

What the activity levels mean

1.2 · Mostly seated

Multiplies your BMR by 1.2. Desk work and little deliberate movement outside training.

1.375 · Lightly active

Multiplies your BMR by 1.375. Light activity most days, or one to three training sessions a week.

1.55 · Moderately active

Multiplies your BMR by 1.55. Three to five training sessions a week plus normal daily movement. This is the default.

1.725 · Very active

Multiplies your BMR by 1.725. Six or more sessions a week, or physically demanding work.

How big the deficit or surplus is

Pace changes the size of the adjustment, not the equation.

Steady & sustainable

Fat loss: -375 kcal from maintenance. Muscle building: +225 kcal. General fitness applies no adjustment at any pace.

Gentle / low pressure

Fat loss: -250 kcal from maintenance. Muscle building: +150 kcal. General fitness applies no adjustment at any pace.

Ambitious

Fat loss: -500 kcal from maintenance. Muscle building: +325 kcal. General fitness applies no adjustment at any pace.

Why this differs from other calculators

Three things move the number, and calculators rarely agree because they make different choices about each. First, the equation: some still use Harris Benedict, which tends to read higher. Second, the activity multiplier, where one tool's "moderate" is another's "light". Third, the size of the deficit, which is a judgement call rather than a calculation.

Any of these is an estimate of a real number that varies between people of identical size. Treat the output as a starting point, then adjust from what actually happens to your weight over two weeks.

What to do with the number

Hold it for a fortnight and track the trend rather than a single morning's reading. If fat loss has stalled after two weeks of consistent eating, reduce by about 100 kcal or add daily movement. If you are gaining more than roughly half a kilo a week while building, ease the surplus back.

To turn this into meals and training, the macro calculator splits the target into protein, carbohydrate and fat, and the calorie guide works through the whole method with an example.

Related: Macro calculator · Protein calculator · How many calories do I need? · Fat loss plan