Weight Loss Calculator (timeline + target date)

How the math works

1 kg of body fat ≈ 7,700 kcal of energy. To lose 1 kg, you need a cumulative caloric deficit of ~7,700 kcal. So a daily deficit of 500 kcal × 14 days = 7,000 kcal ≈ 0.9 kg per 2 weeks, or about 0.45 kg/week. The famous '500 kcal deficit = 1 lb (0.45 kg) per week' rule comes from this.

Real-world results vary. Water weight fluctuates ±1-2 kg daily based on hydration, glycogen, sodium, and food in the digestive tract. The fat-loss math is reliable over weeks-to-months timeframes; daily scale readings are too noisy.

Safe deficit ranges

Conservative (250 kcal/day): ~0.23 kg/week. Slow, sustainable, minimal hunger and metabolic adaptation. Best for those near their goal weight or with little weight to lose.

Standard (500 kcal/day): ~0.45 kg/week. The textbook recommendation for most people. 1 lb/week loss is well-tolerated and sustainable for months.

Aggressive (750-1000 kcal/day): ~0.7-0.9 kg/week. Faster but harder to sustain. More hunger, more metabolic adaptation. Most professionals cap deficits at 25% below TDEE for sustainability — 1000 kcal/day below a 2000 TDEE is 50%, too aggressive long-term.

Why actual results often differ from math

Metabolic adaptation: with sustained deficit, your BMR drops 5-15% as your body conserves energy. The same '500 kcal deficit' becomes effectively 350 kcal as the metabolism adapts.

Tracking accuracy: studies show people under-report calorie intake by 20-30% even when actively logging. If your weight isn't moving as predicted, the most likely cause is more calories than you think (untracked drinks, larger portions, etc.).

Lean mass loss: aggressive deficits cause up to 25% of weight loss to come from muscle, not fat. Strength training and adequate protein (1.6-2.2 g/kg of bodyweight) protect lean mass. Slow loss + lifting = mostly fat lost; rapid loss without lifting = mostly muscle lost.