Formula, in Fat Loss
Calorie Deficit Formula
A pound of stored fat is roughly 3,500 calories. Spread a deficit across a week (500/day → ~1 lb/week) and metabolic adaptation stays manageable; chase faster losses and lean mass takes a hit.
3 variables. Published Mar 12, 2026. Updated May 10, 2026. By AI Fit Hub.
weekly_fat_loss_kg = (TDEE − intake) × 7 / 7,700
10% deficit = TDEE × 0.90 = a sustainable cut
20% deficit = TDEE × 0.80 = upper end before muscle starts to suffer Variables
TDEE
Maintenance calories
Total Daily Energy Expenditure. From BMR × activity factor or measured over 2–3 weeks of stable weight.
intake
Daily calorie intake
Average daily consumption. Tracked accurately requires weighing food for at least the first month.
7,700
Calories per kg of fat
Energy density of stored adipose tissue. 3,500 cal per pound. Note: actual body-weight loss includes water, glycogen, and lean mass — not just fat.
Step by step
- 1
Establish TDEE through 2–3 weeks of stable weight at a known intake. Calculator estimates are starting points, not endpoints.
Maintenance lands at 2,710 cal/day.
- 2
Pick a deficit size: 10–15% for sustainable long-term loss, 20% for time-boxed cuts under 12 weeks.
15% deficit: 2,710 × 0.85 = 2,303 cal/day target.
- 3
Calculate the daily energy gap.
2,710 − 2,303 = 407 cal/day deficit.
- 4
Project weekly loss: deficit × 7 / 7,700.
407 × 7 / 7,700 = 0.37 kg/week. Or 0.81 lb/week — a sustainable pace.
Worked example
TDEE 2,710, 15% deficit
TDEE
2,710
Target intake
2,303
Deficit
407 cal/day
weekly_loss = 407 × 7 / 7,700 = 2,849 / 7,700 = 0.37 kg/week
Expected loss ~0.37 kg/week (0.8 lb). Over 12 weeks: ~4.4 kg. Adjust intake every 2–3 weeks as TDEE drops with body mass.
Common variations
Run the numbers next
- Nutrition TDEE Calculator
Estimate your daily energy expenditure with Mifflin-St Jeor + activity factors.
- Planning Body Recomposition Planner
Plan body-fat reduction pace, deficit targets, and protein needs around a timeline.
Questions people ask next
How many calories are in a pound or kilogram of fat?
A pound of stored body fat is roughly 3,500 calories, and a kilogram is about 7,700 calories. These are static approximations for the energy density of stored adipose tissue. Actual body-weight loss also includes water, glycogen, and some lean mass, so the scale moves faster than fat alone at first.
How big should my calorie deficit be?
Use 10-15% below maintenance for sustainable long-term loss, and up to 20% for a time-boxed cut under 12 weeks. A 10% deficit is TDEE x 0.90; a 20% deficit (TDEE x 0.80) is the upper end before muscle starts to suffer. Chasing faster losses costs lean mass.
How do I calculate my weekly fat loss from a daily deficit?
Weekly fat loss in kg = (TDEE − intake) x 7 / 7,700. For example, a 407 cal/day deficit gives 407 x 7 / 7,700 = 0.37 kg/week, about 0.8 lb. A 500 cal/day deficit works out to roughly 1 lb per week.
Why does my weight loss slow down over time on a deficit?
As you lose body mass your TDEE drops, so the same intake produces a smaller gap and slower loss; metabolic adaptation also plays a role. The fix is to re-establish maintenance and adjust intake every 2-3 weeks. The 3,500 cal/lb rule is a static approximation, while dynamic models like Hall-Kevin's account for this adaptation.
Does carb cycling or a cyclic deficit make fat loss faster?
No. A cyclic deficit (for example 5 days deficit plus 2 days maintenance) can preserve performance better in athletes, but it does not accelerate fat loss. Total weekly energy balance is what drives the result.
Sources
- Hall KD. What is the required energy deficit per unit weight loss? , International Journal of Obesity (2008)
- Trexler ET et al. Metabolic adaptation to weight loss: implications for the athlete , Journal of the International Society of Sports Nutrition