Calorie Deficit Calculator
Pick a goal weight and a timeline — get the exact daily calories to hit it, with a safety check and projection chart.
How a calorie deficit works
A pound of body fat stores roughly 3,500 kcal (about 7,700 kcal per kg). Eat 500 kcal under your TDEE every day and you create a 3,500 kcal weekly gap — about one pound of loss per week. This calculator works backwards: goal weight + deadline → required daily calories.
What pace is safe?
- Sustainable: 0.5-1% of body weight per week — enough to see progress, gentle enough to keep muscle and sanity.
- Aggressive: 1-1.5% per week works short-term for higher body fat, with high protein and lifting.
- Red line: intake below 1,500 kcal (men) / 1,200 kcal (women) — the calculator flags this automatically.
Why loss slows over time
As you shrink, your TDEE shrinks: a lighter body burns fewer calories, and metabolism adapts a few percent beyond that. The straight line in the chart is a first-order estimate — expect the real curve to flatten. Recalculate every 10-15 lb, and consider maintenance breaks every 8-12 weeks of dieting.
Frequently asked questions
How big should my calorie deficit be?
A 500 kcal/day deficit — about 1 lb per week — is the sweet spot for most people. Push to 750-1,000 only if you have substantial weight to lose and your intake stays above the safe floor.
How long until I lose 20 pounds?
At a sustainable 1-1.5 lb per week, plan on 3-5 months. The calculator lets you test any timeline and instantly shows whether the required calories remain safe.
Why is a 3,500-calorie deficit not exactly one pound?
The 3,500 rule is a useful approximation. Early loss includes water and glycogen, later loss meets metabolic adaptation, so real-world results run 10-20% behind the straight-line math over months.
Should I do cardio or just eat less?
Both work — the deficit is the mechanism either way. Combining a modest food deficit with activity preserves more muscle, improves fitness, and beats either extreme for adherence.
References
- Wishnofsky M. Caloric equivalents of gained or lost weight. Am J Clin Nutr, 1958.
- Hall KD, et al. Quantification of the effect of energy imbalance on bodyweight. Lancet, 2011.
- Helms ER, et al. Evidence-based recommendations for natural bodybuilding contest preparation. JISSN, 2014.