Free calculator

Calorie deficit calculator

This calculator gives you a daily calorie target for weight loss, plus a protein target, a fibre minimum and an estimate of how fast you will lose. Enter your sex, age, height, weight, activity and preferred pace.

How it's calculated

Resting energy comes from the Mifflin–St Jeor equation (Mifflin et al., 1990): 10 × weight (kg) + 6.25 × height (cm) − 5 × age, plus 5 for men or minus 161 for women. It is multiplied by 1.375, 1.55 or 1.725 for low, moderate or high daily activity to estimate maintenance calories.

Your pace sets the deficit: 275, 550 or 825 kcal a day, capped at 25% of maintenance. The target never drops below 1,200 kcal for women or 1,500 kcal for men. Weekly loss is estimated with about 7,700 kcal per kg, and the calculator shows how many weeks 5 kg would take at that rate.

Protein is 1.8 g per kg of body weight. If you weigh more than 20% above the Devine ideal weight for your height, it uses an adjusted weight (ideal weight plus 40% of the difference), capped at 200 g. Fibre is 14 g per 1,000 kcal, with a minimum of 25 g. People who train three or more times a week get 2.0 g/kg in the full meal plan.

Any equation is an estimate. Individual metabolism can differ from the prediction by a few hundred calories, so use the result as a starting point and adjust after 3 weeks of weigh-ins.

Frequently asked questions

How accurate is the Mifflin–St Jeor equation?

It is one of the better-validated equations for healthy adults and is widely used by dietitians, but it predicts an average. Your real maintenance may be a few hundred calories higher or lower. Your weigh-in trend is the final check.

Should I eat back calories from exercise?

Not separately. The activity factor already includes your usual exercise, so adding exercise calories on top would count them twice. If you start training much more than before, rerun the calculator with a higher activity level instead and watch your weekly average weight.

Why is there a minimum calorie target?

Very low intakes make it hard to get enough protein, fibre and micronutrients, and they increase muscle loss, hunger and fatigue. The 1,200 and 1,500 kcal floors are common safety limits for unsupervised dieting; going lower needs medical supervision.

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General fitness information, not medical advice. Check with a doctor if you have a medical condition, are pregnant or have an injury.