How to Calculate a Calorie Deficit (the Formula Apps Use)
Updated October 3, 2026. This is the exact method the TrackAI app uses to set your daily target. It is general information for healthy adults, not medical advice.
A calorie deficit is the gap between the energy you burn and the energy you eat. Eat less than you burn and your body makes up the difference from its stores. To set one, you need three numbers: what you burn, how fast you want to go, and a safe floor.
Step 1: your basal metabolic rate (BMR)
BMR is what your body burns at rest. The Mifflin-St Jeor equation is the most widely used estimate:
- Men: 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5
- Women: 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161
Step 2: multiply by your activity
Your total daily energy expenditure (TDEE), or maintenance calories, is BMR times an activity factor. TrackAI asks how many workouts you do per week:
| Workouts per week | Factor |
|---|---|
| 0–2 | 1.375 |
| 3–5 | 1.55 |
| 6 or more | 1.725 |
Step 3: turn a weekly pace into a daily deficit
One kilogram of body weight is about 7,700 kcal (one pound about 3,500 kcal). So:
Daily deficit = weekly pace × 7,700 ÷ 7 (or pace in lb × 3,500 ÷ 7)
Losing 0.5 kg a week means about 550 kcal a day below maintenance; 1 kg a week means about 1,100.
Step 4: apply a safe floor
Subtract the deficit from your TDEE. If the result is below 1,500 kcal for men or 1,200 kcal for women, use the floor instead and accept a slower pace.
Step 5: set protein first, then split the rest
When you eat less, protein protects muscle. TrackAI sets protein to at least 2.0 g per kg of body weight when losing (1.4 g/kg when maintaining, 1.8 g/kg when gaining), or your diet's protein share if that is higher. The remaining calories are split between carbs (4 kcal per gram) and fat (9 kcal per gram) in your diet's ratio; for a balanced diet that is 50 : 30.
A worked example
A 35-year-old woman, 165 cm and 75 kg, who trains 3–5 times a week and wants to lose 0.5 kg a week:
- BMR = 10 × 75 + 6.25 × 165 − 5 × 35 − 161 = 1,445 kcal
- TDEE = 1,445 × 1.55 = 2,240 kcal
- Deficit = 0.5 × 7,700 ÷ 7 = 550 kcal
- Target = 2,240 − 550 = 1,690 kcal (above the 1,200 floor)
- Protein = 2.0 × 75 = 150 g (600 kcal). The remaining 1,090 kcal split 50 : 30 gives about 170 g carbs and 45 g fat.
You can run your own numbers in the calorie calculator, which uses exactly these steps.
Then track it, and adjust
A formula is a starting point. Bodies differ, and activity estimates are rough. Log what you eat for two to three weeks and watch the weekly average of your weight, not single weigh-ins. If it is not moving and your log is honest, take off another 100–200 kcal. If you are losing faster than planned and feel drained, add some back.
That is what TrackAI is for: snap a meal to log it, and the app tracks your calories, protein and the trend line against the target it set. When your weight or activity changes, it recalculates.
FAQ
How big should my calorie deficit be?
For most people, a deficit that loses about 0.25 to 1 kg (0.5 to 2 lb) a week is sustainable. Losing 0.5 kg a week takes roughly 550 kcal a day under maintenance (0.5 × 7,700 ÷ 7). Faster is possible but harder to keep up and more likely to cost muscle.
What is the lowest calorie target that is safe?
TrackAI never sets a target below 1,500 kcal a day for men or 1,200 kcal for women, the floors most mainstream trackers use. Going lower should be supervised by a doctor.
How much protein should I eat in a deficit?
TrackAI sets at least 2.0 g of protein per kg of body weight when you are losing weight, because a high protein intake helps you keep muscle and stay full on fewer calories.