Fat Loss Formula

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 VARIABLESPublished Mar 12, 2026Updated May 10, 2026Live Content

By Orbyd Editorial · AI Fit Hub Team

Best Next MovePlanning

Calorie Deficit Calculator

Estimate required daily calorie deficit for a target timeline and bodyweight change.

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Formula 3 variables Worked example Variations

Education · Not medical advice. Output is deterministic math from your inputs.Editorial standards Sponsor disclosure Corrections

Formula

Copy the exact expression or work through it step by step below.

 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

Hall-Kevin dynamic model accounts for metabolic adaptation; 3,500 cal/lb is a static approximation.

Cyclic deficit (e.g., 5 days deficit + 2 days maintenance) preserves performance better in athletes but doesn't accelerate fat loss.

Protein-sparing modified fast: aggressive deficit (40%) with high protein, ≤12 weeks, medical supervision. Specialized — not a default choice.

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Sources & References

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