Hong Life CalculatorsUnderstanding the weight loss calorie deficit calculator — concept and principle
This calculator turns a weekly weight-loss goal into a daily calorie target. It first estimates your total daily energy expenditure (TDEE), then subtracts the deficit needed for your chosen rate, and stops at a safe minimum if the target would go too low.
How it is calculated
- BMR (Mifflin-St Jeor) = 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5 for men, or − 161 for women.
- TDEE = BMR × activity factor (1.2 sedentary, 1.375 light, 1.55 moderate, 1.725 hard).
- Daily deficit = kg per week × 7,700 ÷ 7.
- Daily calories = TDEE − deficit, but not below 1,500 kcal (men) or 1,200 kcal (women). If the floor applies, the note tells you to choose a slower rate.
The principle
Body weight changes when energy in and energy out differ. A kilogram of body fat tissue stores roughly 7,700 kcal (about 3,500 kcal per pound), so losing 0.5 kg a week needs about 3,850 kcal less per week, or 550 kcal a day. The Mifflin-St Jeor equation is one of the most accurate predictive formulas for resting energy in healthy adults; the activity factor scales it up to cover daily movement, exercise and the thermic effect of food.
Worked example
- Inputs: male, 35 years, 75 kg, 175 cm, light activity (1.375), 0.5 kg per week.
- BMR = 750 + 1,093.75 − 175 + 5 = 1,673.75 kcal.
- TDEE = 1,673.75 × 1.375 = 2,301.4, shown as 2,301 kcal.
- Daily deficit = 0.5 × 7,700 ÷ 7 = 550 kcal.
- Daily calories = 2,301.4 − 550 = 1,751.4, shown as 1,751 kcal. That is above 1,500, so the note says OK.
| Height (cm) | Daily calories |
|---|---|
| 43.8 | 1,500 |
| 87.5 | 1,500 |
| 131 | 1,500 |
| 175 | 1,751 |
| 219 | 2,127 |
| 262 | 2,503 |
| 350 | 3,255 |
How to read the result
Many guidelines suggest 0.5–1 kg a week. A larger deficit speeds early loss but increases hunger, muscle loss and the chance of giving up. After a few weeks, compare the real trend of your weekly average weight with the target and adjust by 100–200 kcal. Early in a diet, the scale often drops faster than predicted because glycogen and water are lost.
Common mistakes
- Choosing "hard" activity when most of the day is spent sitting; over-estimating activity is the most common reason for slow progress.
- Judging progress by single daily weigh-ins instead of a weekly average.
- Keeping the same target after losing 5–10 kg; TDEE falls as weight falls.
Frequently asked questions
How accurate is Mifflin-St Jeor?
In studies it predicts resting energy within about 10% for most healthy adults, but individuals can fall outside that range.
Why is there a minimum of 1,200 or 1,500 kcal?
Below these levels it becomes hard to meet protein and micronutrient needs without professional planning.
Should I eat back exercise calories?
Not if your activity factor already includes that exercise; otherwise add back only part, since estimates tend to be high.
Sources: Mifflin MD, St Jeor ST et al. A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition 1990. · Hall KD et al. Quantification of the effect of energy imbalance on bodyweight. The Lancet 2011.