What this calculator does
The Calories to Fat Loss Calculator estimates how much body fat you could lose from a given calorie deficit. Because a kilogram of stored body fat holds approximately 7,700 kilocalories of energy, you can translate the total energy deficit you accumulate over time into an estimated change in body fat — shown in both kilograms and pounds.
How to use it
Enter your average daily calorie deficit (the number of calories you eat below your maintenance level each day) and the number of days you maintain that deficit. The tool multiplies the two to get your total deficit, then divides by 7,700 to estimate kilograms of fat lost and converts that to pounds.
The formula explained
The calculation is simply: $$\text{kg fat} = \dfrac{\text{daily deficit} \times \text{days}}{7700}$$ The constant 7,700 kcal per kilogram (about 3,500 kcal per pound) is the widely used approximation for the energy density of adipose tissue. Real-world results vary because weight change also involves water, glycogen, and muscle, and because metabolism adapts during a diet.
Worked example
Suppose you keep a 500 kcal daily deficit for 30 days. Total deficit = $$500 \times 30 = 15{,}000 \text{ kcal}.$$ Dividing by 7,700 gives about $$\dfrac{15{,}000}{7700} \approx 1.95 \text{ kg}$$ of fat, which is roughly $$1.95 \times 2.2046 \approx 4.3 \text{ lb}.$$ That is a realistic, sustainable rate of fat loss.
FAQ
Why 7,700 calories per kg? It's the long-standing estimate of the energy stored in a kilogram of body fat (3,500 kcal per pound).
Will I really lose exactly this amount? Treat the result as an estimate. Early weight loss often includes water, and the body's energy expenditure drops as you get lighter, so long-term loss tends to be slower.
Can I use it for weight gain? Yes — enter a calorie surplus as the "deficit" value and the result estimates fat gained instead.
