Calorie Deficit Calculator
Work out your maintenance calories and a safe daily deficit for weight loss - in a few seconds.
What a calorie deficit is and how big it should be
A calorie deficit means spending more energy than you take in from food, and it is what drives weight loss. A safe deficit is about 500-1000 kcal a day, which gives roughly 0.5-1 kg per week. The calculator above works out your maintenance calories with the Mifflin-St Jeor formula and offers three deficit tiers - gentle, balanced and fast.
How to calculate a calorie deficit
It is two steps. First find your maintenance calories (TDEE) - basal metabolic rate multiplied by an activity factor. Then subtract a deficit: 15% for a gentle pace, 20% for balanced, 25% for fast (but never below 1200 kcal for women or 1500 for men). One kilogram of fat holds about 7700 kcal, so a 500 kcal daily deficit is roughly 0.5 kg a week.
A deficit for women and men
The formula is the same, but men have a higher basal rate, so both maintenance and the deficit are larger in absolute numbers. A 65 kg woman usually suits a 300-500 kcal deficit, an 80 kg man 500-750 kcal. The safety floor is 1200 kcal for women and 1500 for men.
Keeping muscle in a deficit
Weight on the scale is not always fat: in a deficit, weight often comes off muscle too, which is bad for metabolism and health [3]. Two things protect it: protein above the usual 0.8 g per kg helps retain muscle and lose fat [2], and resistance training signals muscle to stay, though a large, prolonged deficit still limits its growth [1].
Why the scale stalls
Eating even less works badly. Too sharp a deficit triggers metabolic adaptation - the body slows down and the scale stalls. Add water retention, hunger-driven breakdowns and muscle loss, and the result is worse than a moderate deficit. A stall of a week or two on a kept target is usually water, not a broken metabolism. You can create the deficit in different ways: a steady daily deficit and intermittent fasting produce a comparable energy deficit and work similarly [4] - pick what you can keep to.
Frequently asked questions
What calorie deficit do I need to lose weight?
About 500-1000 kcal a day below your maintenance, which gives roughly 0.5-1 kg per week.
How do I calculate a calorie deficit?
Find maintenance (Mifflin-St Jeor BMR times an activity factor) and subtract 15-25%. The calculator above does it for you.
How much can I lose on a calorie deficit?
With a 500-1000 kcal daily deficit, about 0.5-1 kg a week. A sharper deficit is faster but risks muscle loss and breakdowns.
Why does my weight stall in a deficit?
Usually water retention and metabolic adaptation. On a kept target the scale normally moves again within one or two weeks.
How do I avoid losing muscle?
Keep protein above 0.8 g per kg of body weight and add resistance training, so the weight comes off fat rather than muscle.
Sources
- Energy deficiency impairs resistance training gains in lean mass but not strength. Scand J Med Sci Sports, 2022. PubMed
- Protein Recommendations for Weight Loss in Elite Athletes. Int J Sport Nutr Exerc Metab, 2018. PubMed
- Body Composition Changes in Weight Loss. Nutrients, 2018. PubMed
- Is Fasting Superior to Continuous Caloric Restriction for Weight Loss. Nutrients, 2024. PubMed
This tool gives an estimate and does not replace medical advice. During pregnancy, breastfeeding, eating disorders, diabetes or other conditions, plan your diet with a clinician.