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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 AI Fit Hub · 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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On This Page

Formula 3 variables Worked example Variations

Education · Not medical advice. Output is deterministic math from your inputs.Editorial standardsSponsor disclosureCorrections

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. 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. 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. 3

    Calculate the daily energy gap.

    2,710 − 2,303 = 407 cal/day deficit.

  4. 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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FAQ

Questions people ask next

The short answers readers usually want after the first pass.

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 & References

General fitness estimates — not medical advice. Consult a healthcare professional for medical decisions.