How Calories Affect Your Weight
Your weight changes based on the relationship between calories consumed and calories burned. This is called energy balance:
- Calories in = Calories out â Weight stays the same
- Calories in < Calories out â Weight decreases (fat loss)
- Calories in > Calories out â Weight increases
One kilogram of body fat contains approximately 7,700 kilocalories (one pound â 3,500 kcal). To lose 1 kg of fat, you need a cumulative deficit of 7,700 kcal â achievable in 2â4 weeks at a safe 500â1,000 kcal/day deficit.
Step 1 â Calculate Your BMR
Your Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest â just to keep your organs running. This is typically 60â75% of your total daily calorie burn.
The most accurate BMR formula for non-athletes is the Mifflin-St Jeor equation (1990), validated by the American Council on Exercise:
For Men:
BMR = (10 Ã kg) + (6.25 Ã cm) â (5 Ã age) + 5
For Women:
BMR = (10 Ã kg) + (6.25 Ã cm) â (5 Ã age) â 161
Example (male, 30 years, 75 kg, 178 cm):
BMR = (10Ã75) + (6.25Ã178) â (5Ã30) + 5 = 750 + 1112.5 â 150 + 5 = 1,717 kcal/day
Step 2 â Calculate Your TDEE
Your Total Daily Energy Expenditure (TDEE) accounts for your activity level on top of BMR. Multiply your BMR by the appropriate activity factor:
| Activity Level | Description | Multiplier | Example TDEE (BMR=1717) |
|---|---|---|---|
| Sedentary | Desk job, no exercise | Ã 1.2 | 2,060 kcal |
| Lightly Active | Light exercise 1â3 days/week | Ã 1.375 | 2,361 kcal |
| Moderately Active | Moderate exercise 3â5 days | Ã 1.55 | 2,661 kcal |
| Very Active | Hard exercise 6â7 days | Ã 1.725 | 2,962 kcal |
| Extra Active | Physical job + daily exercise | Ã 1.9 | 3,262 kcal |
Step 3 â Set Your Calorie Deficit
Subtract your target deficit from your TDEE to get your daily calorie target for weight loss:
Daily calorie target for weight loss:
Calorie Target = TDEE â Deficit
Example: TDEE of 2,400 kcal â 500 kcal deficit = 1,900 kcal/day â loses ~0.5 kg/week
How Many Calories Per Day to Lose Weight?
Use this general reference table. These are estimates â your individual TDEE will vary based on body composition:
| Goal | Women (approx.) | Men (approx.) | Weekly Loss |
|---|---|---|---|
| Slow loss | 1,400â1,600 kcal | 1,800â2,000 kcal | ~0.25 kg/week |
| Moderate loss | 1,200â1,400 kcal | 1,600â1,800 kcal | ~0.5 kg/week |
| Faster loss | 1,000â1,200 kcal | 1,400â1,600 kcal | ~0.75 kg/week |
Never go below 1,200 kcal/day for women or 1,500 kcal/day for men without medical supervision. Very low calorie diets cause muscle loss, nutrient deficiencies, and metabolic adaptation.
Weight Loss Timeline
| Weight to Lose | At 0.25 kg/week | At 0.5 kg/week |
|---|---|---|
| 5 kg (11 lbs) | 20 weeks (~5 months) | 10 weeks (~2.5 months) |
| 10 kg (22 lbs) | 40 weeks (~10 months) | 20 weeks (~5 months) |
| 20 kg (44 lbs) | 80 weeks (~18 months) | 40 weeks (~10 months) |
| 30 kg (66 lbs) | 120 weeks (~28 months) | 60 weeks (~14 months) |
Slow, consistent weight loss (0.25â0.5 kg/week) results in far better long-term outcomes than rapid loss. Research shows 80% of rapid weight loss is regained within 5 years, while gradual loss is more permanent.
Calculate Your Personal Calorie Target
Our free Calorie Calculator uses the Mifflin-St Jeor equation to calculate your BMR and TDEE for all 5 activity levels. Instant result â no signup.
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