Calorie Deficit
Calculator.
Find the exact daily calories you need to lose fat — without guessing or crash dieting.
Track your weight, calories, and training in one place — and see if your deficit is actually working.
What is a calorie deficit?
A calorie deficit means eating fewer calories than your body burns in a day. It is the one and only requirement for fat loss: when you consistently take in less energy than you expend, your body makes up the difference by burning stored fat. To find your deficit, you first calculate your maintenance calories (TDEE), then subtract a sensible amount — typically 10–25%.
How big should my deficit be?
For most people a moderate deficit of around 20% below maintenance (roughly 500 kcal) is the sweet spot — fast enough to see steady progress, slow enough to preserve muscle and adherence. Roughly 7,700 kcal equals 1 kg of body fat, so a 500 kcal daily deficit produces about 0.5 kg of fat loss per week. If your main goal is recomposition (building muscle while losing fat), a smaller deficit of 200–300 kcal is often better.
How is this calculated?
This calculator uses the Mifflin-St Jeor equation to estimate your basal metabolic rate (BMR), multiplies it by an activity factor to get your TDEE, then subtracts each deficit level. The Mifflin-St Jeor formula is considered the most accurate BMR equation for most people and is recommended by the Academy of Nutrition and Dietetics.
Don't forget protein
In a deficit, adequate protein is what protects your muscle. The landmark meta-analysis by Morton et al. (2018) found muscle gains plateau around 1.6 g protein per kg bodyweight, with ~2.2 g/kg as a safe upper target. When cutting, aim for the higher end (1.8–2.2 g/kg) to minimise muscle loss while you drop fat.
Track your deficit with reppd
A calculator gives you a starting number — but real progress comes from tracking. reppd tracks your body weight over time with trend analysis, so you can see whether your deficit is actually working and adjust before you stall. Combine it with workout tracking and your TDEE for the full picture — all end-to-end encrypted.
Want to lose fat without losing muscle? Read our guide to body recomposition — building muscle in a calorie deficit.