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A calorie deficit means you eat less energy than your body burns. To lose fat without losing muscle, a sensible deficit is one where you lose 0.5 to 1% of your body weight a week. For most people, that is 300 to 700 kcal a day below maintenance. On top of that, eat 1.8 to 2.7 g of protein per kilogram and do strength training.
Calorie calculator
Lose fat (−0.5 % a week)
2,245
kcal/day
Maintain weight
2,685
kcal/day
Build muscle (+250 kcal)
2,935
kcal/day
Estimate. Your real number shows after 2–3 weeks of logging food and weight.
How to calculate your deficit
- Maintenance calories. The calculator above estimates them with the Mifflin–St Jeor equation, one of the most accurate for the general population.1 The result is then multiplied based on your activity level.
- Deficit. To lose 0.5% of your body weight a week, subtract roughly what the calculator shows you, usually 300 to 600 kcal.
- Check-in. After 2 to 3 weeks, compare your weekly average weights. If your weight is dropping too slowly or too fast, adjust your intake by 100 to 200 kcal.
Every calculator is just an estimate. The best way to find your real expenditure is to log your food and weight for 2 to 3 weeks.
How fast to lose weight
Faster is not better. In a study of athletes, the group that lost weight more slowly, about 0.7% of body weight a week, gained strength and kept more muscle than the group losing at a faster 1.4% a week.2 That is why guidelines for strength sports recommend 0.5 to 1% of body weight a week.3
| Your weight | 0.5% a week | 1% a week |
|---|---|---|
| 60 kg | 0.3 kg | 0.6 kg |
| 80 kg | 0.4 kg | 0.8 kg |
| 100 kg | 0.5 kg | 1.0 kg |
If you have more weight to lose, the upper end is fine. If you are already lean and want to get shredded, stay closer to the lower end.
How to keep your muscle
- Protein: 1.8 to 2.7 g per kilogram. In a deficit, your body needs more protein than at maintenance.4 It also keeps you fuller.
- Keep strength training. Training signals your body to hold on to muscle. You don't need to do more. Just keep the intensity up, which means heavy weights.
- Sleep at least 7 hours. In a study combining a deficit with short sleep, people lost half as much fat and more lean mass than with enough sleep.6
- Steps. Extra walking raises your expenditure without hurting your recovery from training.
Why weight loss slows down
The old rule says 7,700 kcal is 1 kg of fat, so a 500 kcal daily deficit means 0.5 kg a week forever. In reality, your energy expenditure drops as your weight drops. A smaller body burns less, and your body partly adapts.5
That is why weight loss slows after a few weeks or months, even if you keep eating the same. It is not a mistake or a "broken metabolism." Just recalculate your intake for your new weight or add more movement.
Why the scale jumps around
Your weight can change by 1 to 2 kg from one day to the next. The cause is water, salt, carbs, gut contents or your menstrual cycle. Fat does not change overnight.
So weigh yourself in the morning, after using the toilet, before eating, and track your weekly average. Only adjust your intake once the average hasn't moved for two weeks.
Frequently asked questions
Do I have to count calories?
You don't have to, but it helps a lot at the start. After 2 to 3 weeks of logging, you get a feel for portion sizes, and after that you can eat more by estimate.
What is the largest safe deficit?
For most people, no more than about 25% of maintenance calories. Very strict diets below 1,200 kcal should be done under professional supervision.
Can I lose fat and build muscle at the same time?
Beginners and people with higher body fat can, especially with high protein and strength training. For advanced lifters it happens much more slowly.
What is the best food for weight loss?
The food you can stick with long term. Protein, vegetables, legumes and whole grains help, because they keep you full on fewer calories.
References
- 1.Mifflin MD et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241–247. doi:10.1093/ajcn/51.2.241
- 2.Garthe I et al. Effect of two different weight-loss rates on body composition and strength and power-related performance in elite athletes. Int J Sport Nutr Exerc Metab. 2011;21(2):97–104. doi:10.1123/ijsnem.21.2.97
- 3.Helms ER, Aragon AA, Fitschen PJ. Evidence-based recommendations for natural bodybuilding contest preparation: nutrition and supplementation. J Int Soc Sports Nutr. 2014;11:20. doi:10.1186/1550-2783-11-20
- 4.Helms ER et al. A systematic review of dietary protein during caloric restriction in resistance trained lean athletes: a case for higher intakes. Int J Sport Nutr Exerc Metab. 2014;24(2):127–138. doi:10.1123/ijsnem.2013-0054
- 5.Hall KD et al. Quantification of the effect of energy imbalance on bodyweight. Lancet. 2011;378(9793):826–837. doi:10.1016/S0140-6736(11)60812-X60812-X)
- 6.Nedeltcheva AV et al. Insufficient sleep undermines dietary efforts to reduce adiposity. Ann Intern Med. 2010;153(7):435–441. doi:10.7326/0003-4819-153-7-201010050-00006
This article is for general information and does not replace advice from a doctor or registered dietitian. If you have a health condition, talk to a professional before changing your training, diet or supplements.
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