Calorie Deficit Calculator
Find your maintenance calories and the daily calorie target that makes you lose weight — using the Mifflin-St Jeor formula dietitians rely on.
How the calorie deficit formula works
A calorie deficit means eating fewer calories than your body burns in a day. Your body makes up the difference from stored fat — that is what weight loss is.
This calculator uses the Mifflin-St Jeor equation, the formula with the best accuracy record in clinical comparisons: BMR = 10×weight(kg) + 6.25×height(cm) − 5×age + 5 (men) or −161 (women). Your BMR is then multiplied by an activity factor (1.2–1.9) to get your maintenance calories — the amount you burn per day.
Subtract 250–750 kcal from maintenance and you have your daily target. One kilogram of body fat stores roughly 7,700 kcal, so a 500 kcal daily deficit works out to about half a kilo (one pound) per week.
Calorie deficit — frequently asked questions
What is a calorie deficit?
A calorie deficit is when you consume fewer calories than your body burns per day. Your body covers the missing energy from stored fat, which is how you lose weight. It is the mechanism behind every diet that works.
How do I calculate my calorie deficit?
First find your maintenance calories (BMR × activity factor — the calculator above does this with the Mifflin-St Jeor formula), then subtract 250–750 kcal. The result is your daily calorie target for weight loss.
Is a 500 calorie deficit per day good?
A 500 kcal daily deficit is the most commonly recommended starting point: it produces roughly 0.5 kg (1 lb) of loss per week and is sustainable for most people without extreme hunger or muscle loss.
How much weight will I lose with a 500 calorie deficit?
About 0.5 kg (1 lb) per week, since 1 kg of body fat stores roughly 7,700 kcal. Real-world results vary with water weight, adherence and metabolic adaptation, so treat it as a solid average over several weeks.
Can a calorie deficit be too big?
Yes. Deficits above ~1,000 kcal/day increase muscle loss, fatigue and rebound risk, and are hard to sustain. Unless supervised by a professional, stay in the 250–750 kcal range and never eat below your BMR for long periods.
Knowing your number is easy. Tracking it is the hard part.
Caloryx logs your calories from a single photo of your meal — so staying inside your deficit takes seconds, not spreadsheets.