Calorie Deficit Calculator
How long a daily calorie deficit takes to hit a weight-loss goal.
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Sustainable fat loss comes down to a consistent calorie deficit held over weeks, not crash dieting. This tool turns a daily deficit and a goal into a realistic timeline so you can plan around it instead of guessing.
How it works
About 3,500 calories equal one pound of fat, so a daily deficit of D calories loses D×7÷3500 pounds per week. Time to the goal is goal×3500÷D days.
The math leans on the long-standing rule that about 3,500 calories equal one pound of body fat. A deficit can come from eating less, moving more, or both — the calculator only cares about the net daily gap, not how you create it.
Larger deficits finish faster on paper but get harder to hold and risk muscle loss and rebound hunger. Most people do best with a 300-700 calorie daily deficit, which targets roughly 0.5-1.5 lb of loss per week.
Pounds per week = daily deficit × 7 ÷ 3,500. Days to goal = pounds to lose × 3,500 ÷ daily deficit.
Worked examples
A 500-calorie daily deficit with a 20 lb goal. → 1.00 lb per week, about 140 days (20.0 weeks).
500 × 7 ÷ 3,500 = 1 lb/week; 20 × 3,500 ÷ 500 = 140 days.
A 750-calorie daily deficit with a 10 lb goal. → 1.50 lb per week, about 47 days (6.7 weeks).
750 × 7 ÷ 3,500 = 1.5 lb/week; 10 × 3,500 ÷ 750 ≈ 46.7 days.
Tips & gotchas
- Track an honest baseline for a week before setting a deficit — most people underestimate what they eat by several hundred calories.
- Weigh yourself at the same time daily and judge progress on the weekly average, since water swings can hide real fat loss for days.
- If the scale stalls for two-plus weeks while you're compliant, your maintenance has dropped; recalculate from your new weight.
- Keep protein high and add resistance training so the weight you lose is fat, not muscle.
FAQ
Is 3,500 calories per pound exact?
It's a long-standing estimate, not a precise law — actual loss varies with body composition and adaptive metabolism. Treat it as a planning guide.
Why is my real weight loss slower than the estimate?
The 3,500-calorie model ignores metabolic adaptation, water retention, and logging errors. Use the projected timeline as a planning target and adjust based on your actual weekly average.
Can I just use a huge deficit to finish faster?
You can, but very aggressive deficits cost muscle, tank energy and adherence, and often end in rebound eating. A moderate deficit you can sustain almost always wins over months.
Does the source of the deficit matter?
For weight loss, only the net gap matters. For body composition and health, the food quality, protein, and whether you train do matter a great deal.
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