FitCiIn this article
- What a calorie deficit is and why everything depends on it
- Step 1: Calculate your basal metabolic rate
- Step 2: Find your total daily expenditure (TDEE)
- Step 3: Choose the size of the deficit
- Step 4: Raise protein, keep fat above the floor
- Step 5: Read the scale correctly and adjust every two weeks
- Plateaus: what is happening when the scale stops
- Five common mistakes
What a calorie deficit is and why everything depends on it
When the energy you take in is below your total daily energy expenditure (TDEE), you are in a calorie deficit. The body covers the shortfall from its stores: ideally fat, in a badly built deficit muscle too. Whatever diet you follow (low carb, intermittent fasting, Mediterranean), weight loss comes from the deficit; diets differ in how easy they make it to keep.
One kilogram of fat holds roughly 7,700 kcal. A 500 kcal daily deficit is ~3,500 kcal a week, about 0.45 kg of fat in theory. In practice the first weeks drop faster through water and glycogen, then slow down; that is normal.
Step 1: Calculate your basal metabolic rate
BMR is the energy spent at complete rest for vital functions. The most accurate general formula is Mifflin-St Jeor:
- Men: 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
- Women: 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161
Example: a 32-year-old woman, 172 cm, 84 kg → 840 + 1,075 − 160 − 161 = 1,594 kcal. The BMR calculator shows two formulas side by side if you prefer not to do it by hand.
Step 2: Find your total daily expenditure (TDEE)
Multiply BMR by an activity factor:
| Lifestyle | Factor |
|---|---|
| Desk job, no training | 1.2 |
| 1–3 workouts a week | 1.375 |
| 3–5 workouts a week | 1.55 |
| 6–7 workouts or a physical job | 1.725 |
Our example trains three times a week → 1,594 × 1.375 ≈ 2,190 kcal. Important: the factors systematically overestimate; if unsure, pick one step lower. The formula is the start, the scale is the truth.
Step 3: Choose the size of the deficit
| Deficit | Weekly loss | Who |
|---|---|---|
| 10–15% (≈250–350 kcal) | 0.25–0.35 kg | Lean or normal weight, muscle-focused, long term |
| 20% (≈500 kcal) | ~0.5 kg | The best balance for most people |
| 25–30% (≈750 kcal) | 0.7–0.9 kg | High body fat, short phases, with high protein |
Example: 2,190 − 500 = 1,690 kcal/day. Two safety rules: do not go below 1,200 kcal for women or 1,500 for men (micronutrients and muscle), and do not aim for weight loss with a BMI under 18.5. The calorie calculator does these three steps at once and gives a macro starting point.
Step 4: Raise protein, keep fat above the floor
Protein is the one nutrition decision that prevents muscle loss in a deficit: 2.0 g per kg (~170 g at 84 kg). That is higher than the 1.6 g/kg at maintenance because, with energy scarce, the body also uses protein as fuel. Keep fat at or above 25% of calories (hormone production); the rest goes to carbohydrate. The macro calculator splits it for you; food sources are in the protein guide.
If your BMI is above 30, base protein on your target weight (the weight at BMI 25), not your current weight; fat mass does not create protein needs.
Step 5: Read the scale correctly and adjust every two weeks
Daily weight swings 1–2 kg with water, salt, carbs and gut contents. Weigh every morning under the same conditions and compare weekly averages. If the two-week average falls slower than planned, cut another 100–150 kcal; if faster, add some. This loop is called adaptive TDEE and corrects the formula's error with real data. The FitCi app does it weekly and automatically.
Waist circumference and progress photos mislead less than the scale; if you lift, the scale can stall while the waist shrinks. The body fat calculator estimates from three tape measurements.
Plateaus: what is happening when the scale stops
- The deficit closed. Losing weight lowers TDEE (less mass, less expenditure); after 8 kg your old deficit is no longer a deficit. Recalculate.
- Logging drift. Oils, sauces, snacks and "just a taste" add 200–400 kcal a day. Weigh and log everything for one week; photo logging makes it easier.
- Adaptation. In a long deficit, spontaneous movement (NEAT) drops and thyroid and leptin fall. A 1–2 week diet break at maintenance restores both hormones and patience.
Water retention also mimics a plateau: a hard training week, salty food and the menstrual cycle can lift the scale 1–2 kg. Wait for the two-week average before deciding.
Five common mistakes
- A deficit that is too big. 1,000 kcal means fast month one, muscle loss month two, quitting month three.
- Eating back exercise calories. Watch estimates run 20–40% high, and the TDEE factor already includes training.
- Neglecting protein. Low protein plus a deficit equals muscle loss, and muscle loss equals a lower metabolism.
- Weekend compensation. A 500 kcal deficit on weekdays and a 1,500 kcal surplus on weekends sums to zero.
- Liquid calories. Juice, sweet coffee and soft drinks do not fill you up but they count. Switching to water alone creates a 200–300 kcal deficit for many people.
Frequently asked questions
How many calories should I eat to lose weight?
It depends on you; 1,500–1,800 kcal for an average woman and 1,900–2,300 for a man are common bands. The right number is your TDEE minus 500; find it with the calculator and correct every two weeks from your weigh-in average.
How much weight per week is healthy to lose?
0.5–1% of body weight; 0.4–0.8 kg at 80 kg. Faster is mostly water and muscle and does not last.
Can I lose weight without counting calories?
Yes, but something still has to create the deficit: portion control, protein and vegetables first, cutting liquid calories. Counting is the fastest way to see what works; count for a few weeks, then switch to estimates.
Does a calorie deficit work without exercise?
You will lose weight, but part of it will be muscle and your metabolism will drop. Two or three lifting sessions a week steer the loss toward fat; cardio is optional.
Related tools and pages
FitCi recalculates your deficit every week
Tell it your goal; it finds your calories, scales your meal plan and corrects weekly from your weigh-ins. Log by photo, stop counting.