Estimate calories burned at rest.
Resting energy expenditure is what the body spends simply staying alive — heartbeat, breathing, temperature, cell turnover — and it accounts for roughly 60-70% of most people's daily burn. It is not estimated from activity but from body size, age and sex, using the Mifflin-St Jeor equation, which is the predictive equation that validation studies have found most accurate for the general population. No exercise input belongs in it: adding activity would make it a total daily expenditure figure instead.
Mifflin-St Jeor
REE = 10 x weight(kg) + 6.25 x height(cm) - 5 x age + 5 for men, -161 for women
Derived rates
Per hour = REE / 24; per kg = REE / weight
These are educational and reference calculations only. They are not a diagnosis, not a substitute for measurement or laboratory testing, and must not be used to start, stop, time or change any medication or treatment. Reference thresholds differ between national guidelines and do not account for your individual clinical context. Discuss any result that concerns you with a qualified healthcare professional, and seek urgent medical attention for acute symptoms rather than relying on a calculator.
With the Mifflin-St Jeor equation: 10 x weight in kg + 6.25 x height in cm - 5 x age, then +5 for men or -161 for women. Body size and age set the figure; activity is deliberately excluded because this is the resting baseline.
It is the floor of your energy needs and the base that every activity multiplier is applied to. Eating below it for long periods is what makes aggressive deficits unsustainable, and knowing it makes any calorie target far easier to judge.
Basal metabolic rate is measured after an overnight fast at complete rest and runs a few percent below resting expenditure; the two are used interchangeably in practice. Total daily energy expenditure is this figure multiplied by an activity factor of roughly 1.2 to 1.9.