How to Estimate Weekly Fat Loss from Your Calorie Deficit

One of the most useful pieces of information for anyone dieting is knowing how fast to expect results. This calculator answers that question directly: given a specific daily calorie deficit, what is the expected weekly fat loss?

The calculation uses the 7,716 kcal/kg fat tissue conversion:

For a 500 kcal/day deficit: (500 × 7) / 7,716 = 3,500 / 7,716 ≈ 0.45 kg/week (about 1 lb/week).

Why 7,716 kcal/kg?

Human body fat is not pure triglyceride. It contains water, cellular structures, and connective tissue alongside the stored fat. Adipose tissue is approximately 87% fat by weight, and pure fat contains roughly 8,837 kcal/kg. When accounting for the full composition of adipose tissue: 8,837 × 0.87 ≈ 7,688 kcal/kg, rounded in practice to 7,716 kcal/kg (equivalent to 3,500 kcal/lb).

Why Real Progress Often Differs

• Metabolic adaptation: Your TDEE decreases as you lose weight, reducing the effective deficit over time.
• Muscle loss: At aggressive deficits without sufficient protein, some lean mass is lost. This slightly increases the caloric equivalent per kg of tissue lost (less than 7,716 kcal/kg since muscle contains more water than fat).
• Water and glycogen shifts: Early rapid weight loss is largely glycogen depletion and associated water, not fat. Scale weight can drop faster than fat mass for the first 1–2 weeks.

Use this calculator to set realistic weekly expectations, then track actual progress with a 4-week rolling average to filter out day-to-day water fluctuations.