Fat loss
How to calculate your calorie deficit step by step (with examples)
Formula, worked example and an adjustment system. Everything you need to know how much to eat to lose fat without wrecking performance.
Fat loss requires one physiological condition: spending more energy than you take in over a sustained period. Everything else — macro split, meal timing, supplements — affects how you feel and how much muscle you keep, but it does not replace the deficit.
Step 1: estimate your basal metabolic rate
The Mifflin-St Jeor equation is the most reliable for the general population. For men: 10 x weight (kg) + 6.25 x height (cm) − 5 x age + 5. For women: the same formula ending in −161.
Step 2: multiply by your activity factor
| Activity | Factor | Profile |
|---|---|---|
| Sedentary | 1.2 | Desk job, no exercise |
| Light | 1.375 | 2-3 workouts per week |
| Moderate | 1.55 | 4-5 workouts per week |
| High | 1.725 | 6 workouts or physical job |
Worked example
32-year-old woman, 68 kg, 166 cm, training 4 days: BMR = 680 + 1,037 − 160 − 161 = 1,396 kcal. Total expenditure = 1,396 x 1.55 ≈ 2,164 kcal. A moderate 18% deficit ≈ 1,775 kcal per day.
Step 3: pick the size of the deficit
- Small deficit (10-15%): 0.3-0.4% bodyweight per week. Ideal if you want to keep performance and muscle.
- Moderate deficit (18-22%): 0.5-0.7% per week. The sweet spot for most people.
- Aggressive deficit (25-30%): only with supervision, short timelines and high protein.
In practice the number you calculate is a starting point, not a truth. Real expenditure varies with spontaneous activity, sleep and metabolic adaptation.
Step 4: measure and adjust every two weeks
- Weigh yourself every morning fasted and use the weekly average, never a single day.
- Compare two consecutive averages: if you lose less than 0.3% per week, subtract 100-150 kcal.
- If you lose more than 1% per week and lose strength, add 100-150 kcal.
- Keep protein at 1.8-2.2 g per kilo of bodyweight to protect muscle mass.
Tools that make tracking easier
A kitchen scale and a body scale with weekly trend tracking remove most of the estimation error. You do not need anything more expensive than that.
See recommended scales
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Talk to a professional
Do not use aggressive deficits if you are pregnant, breastfeeding, have a history of eating disorders or diabetes, or take medication affecting appetite or blood glucose. In those cases speak to a doctor or registered dietitian first.
Frequently asked questions
- Do I have to count calories forever?
- No. Counting for 4-6 weeks teaches you portion sizes; many people then maintain results with visual control and weekly weigh-ins.
- Can I lose fat and build muscle at once?
- Yes, especially as a beginner or after a layoff, with a small deficit and high protein. For advanced lifters it is much slower.
- What if I stall for three weeks?
- Audit your actual intake log, raise daily steps first, and only then cut 100-150 kcal.
Keep reading
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