Calorie Deficit Calculator with Weight-Loss Timeline
See exactly how long it takes to hit your goal weight at any deficit size. Built around the 3,500 kcal-per-pound rule with metabolic-adaptation correction.
300–500 kcal sustainable
Sustainable
With adaptive thermogenesis
Total deficit needed: 70,000 kcal over 22.2 weeks. Metabolism slows as you lose weight — the dashed line ignores that, the solid line accounts for it.
How this is calculated
One pound of body fat stores roughly 3,500 kcal of energy (Wishnofsky 1958). The simple model says: lose X pounds by accumulating X × 3,500 kcal of deficit.
That model is a useful first approximation, but it ignores adaptive thermogenesis — your metabolism slows as you lose weight. We layer a small adaptation curve on top of the linear projection so the timeline you see better matches reality.
How to use this
- Pick a deficit you can actually sustain — 300–500 kcal/day for most people.
- Aim for ≤25% below TDEE; deeper cuts risk muscle loss and rebound.
- Track weekly average weight, not daily — daily fluctuations are mostly water.
Frequently asked
- It's a useful first-order estimate but ignores adaptive thermogenesis. For losses over 10% bodyweight, expect actual results to be 5–15% slower than the simple model — we factor a small adaptation curve into the timeline.
- 300–500 kcal/day produces ~0.5–1 lb/week loss for most people. Aggressive deficits over 25% of TDEE risk muscle loss and rebound.