Off the Clock Labs

Calorie calculator

Estimate how many calories you burn in a day, and how much to eat to lose weight at a pace you can keep. It uses the Mifflin-St Jeor equation, published in 1990.

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Units
Sex

How the estimate is made

The calculator works in two steps. First it estimates the energy your body uses at rest, with the equation Mifflin, St Jeor and their colleagues published in 1990 after measuring 498 healthy adults:

Men: 10 × weight in kg + 6.25 × height in cm − 5 × age + 5
Women: 10 × weight in kg + 6.25 × height in cm − 5 × age − 161

Then it multiplies that by a factor for how active you are, from 1.2 for little or no exercise to 1.9 for very hard training or a physical job. Those five factors are a convention used across fitness calculators rather than the finding of one study. A 2004 report on human energy needs from the FAO, WHO and UNU uses three broader bands instead, the lowest starting at 1.40, so if you pick 1.2 the estimate may run low.

Turning it into a target

A kilogram of body weight is worth roughly 7,700 kcal, a rule of thumb that goes back to Wishnofsky’s 1958 figure of about 3,500 kcal a pound. Eating 550 kcal a day below your burn makes 3,850 kcal a week, close to half a kilogram. The NHS suggests aiming for 0.5 to 1 kg a week.

Why your number will drift

Treat the result as a starting point. Eat to it for three or four weeks, follow your trend weight rather than single weigh-ins, and adjust. As you lose weight you burn less, so the same meals give a smaller deficit and loss slows. Work the number out again every few kilos. Calorie deficit: how much less to eat explains why the old rule overpromises over the long run.

Sources

  1. Mifflin MD, St Jeor ST and others. A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition, 1990.
  2. FAO, WHO and UNU. Human energy requirements. 2004.
  3. Wishnofsky M. Caloric equivalents of gained or lost weight. American Journal of Clinical Nutrition, 1958.
  4. Hall KD and others. Quantification of the effect of energy imbalance on bodyweight. The Lancet, 2011.
  5. NHS. 12 tips to help you lose weight.

These calculators give estimates for adults, not a diagnosis. Nothing you type leaves this page.