How to calculate your calorie deficit to lose fat without losing muscle
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Losing fat is not eating less at random: it is creating an exact, sustainable calorie deficit. Here is how to calculate it step by step and keep your muscle while you lean down.
A caloric deficit is the only real requirement for losing fat: spending more energy than you consume. Everything else (diet type, meal timing, fasting) are tools to reach that deficit sustainably, but none of them replaces it. The good news is that calculating it is simple and takes only four steps.
Step 1: calculate your basal metabolic rate (BMR)
The Mifflin-St Jeor formula is the most accurate for the general population:
- Men: BMR = 10 x weight(kg) + 6.25 x height(cm) - 5 x age + 5
- Women: BMR = 10 x weight(kg) + 6.25 x height(cm) - 5 x age - 161
That is what your body burns at complete rest.
Step 2: calculate your total expenditure (TDEE)
Multiply your BMR by your activity factor: sedentary x1.2; light activity (1-3 days) x1.375; moderate (3-5 days) x1.55; high (6-7 days) x1.725. The result is your TDEE: the calories that maintain your current weight.
Step 3: apply the right deficit
A deficit of 15-25 per cent below TDEE is the optimal range for losing fat while preserving muscle. An aggressive deficit (over 30 per cent) speeds up the loss but drives muscle catabolism and fatigue.
Recommended rate: lose 0.5-1 per cent of your body weight per week. Faster than that almost always means losing muscle, not just fat.
Step 4: protect your muscle
The deficit determines how much you eat; these three variables decide whether you lose fat or muscle:
- High protein: 1.8-2.2 g/kg/day. It is the number one factor for retaining muscle mass in a deficit.
- Strength training: maintaining the load sends the signal that this muscle is still needed. Without stimulus, the body discards it first.
- Sleep: sleeping less than 6 hours increases muscle loss and hunger (more ghrelin, less leptin).
Adjust as you go
The initial calculation is an estimate. Weigh yourself 3-4 times a week, fasted, and use the weekly average. If you have not dropped in 2-3 weeks, cut 150-200 kcal or add activity. Do not chase the daily number: chase the trend.
Mistakes that stall your deficit
Underestimating what you eat (oils, snacking, drinks) is the most common error: studies show underestimations of 20-40 per cent. Weighing your food for a few weeks recalibrates your perception. Another mistake: compensating for training by eating more. Cardio burns less than you think.
With your deficit calculated and protein and strength work covered, generating the right routine is the final step: the Progrevia generator creates a strength plan adapted to your available days so you lose fat without losing muscle.
How fast to lose: the number that protects muscle
Working out the deficit is half the job. The other half is deciding how fast you come down, and that is where you settle how much muscle you take with it.
Helms, Aragon and Fitschen compiled the evidence-based recommendations for natural bodybuilding preparation in the Journal of the International Society of Sports Nutrition in 2014. Their conclusion on pace is specific: set calories at a level producing body weight losses of roughly 0.5 to 1% per week, precisely in order to maximise muscle retention.
The percentage matters more than the absolute kilos, which is why the recommendation is expressed as a proportion: losing half a kilo a week is a sensible pace at 100 kg and far too aggressive at 55 kg.
| Body weight | 0.5%/week (conservative) | 1%/week (aggressive) | Approximate daily deficit |
|---|---|---|---|
| 60 kg | 300 g | 600 g | 330-660 kcal |
| 70 kg | 350 g | 700 g | 385-770 kcal |
| 80 kg | 400 g | 800 g | 440-880 kcal |
| 90 kg | 450 g | 900 g | 495-990 kcal |
| 100 kg | 500 g | 1,000 g | 550-1,100 kcal |
How to choose between the two columns. If you have plenty of fat to lose and no great urgency about saving every gram of muscle, the upper end is workable and shortens the phase. If you are already fairly lean, have trained for years, or are worried about losing strength, stay at the lower end: the less fat margin you have left, the more expensive every fast kilo becomes.
One warning follows from the same paper: an aggressive deficit only holds up if protein stays high and you keep training with weights. Without those two, coming down fast stops being fat loss and becomes weight loss, which is not remotely the same thing.
- Helms ER, Aragon AA, Fitschen PJ. Evidence-based recommendations for natural bodybuilding contest preparation: nutrition and supplementation. Journal of the International Society of Sports Nutrition. 2014;11:20.
- Morton RW, Murphy KT, McKellar SR, et al. A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. British Journal of Sports Medicine. 2018;52(6):376-384.
Frequently asked questions
How many calories should I eat to lose fat?
Calculate your TDEE and subtract 15-25%. If your TDEE is 2,400 kcal, a moderate deficit is 1,800-2,040 kcal/day. Start conservative and adjust based on your real weekly loss.
How much weight is healthy to lose per week?
Between 0.5% and 1% of bodyweight per week. For 80 kg that is 0.4-0.8 kg/week. Losing faster usually means losing muscle and water, not just fat.
Can I lose fat and build muscle at the same time?
Yes, especially as a beginner, returning after a break, or with fat to lose. It is called body recomposition and needs high protein, strength training and a small deficit or maintenance.