Calorie Deficit Calculator
Plan a safe fat loss timeline. Compare mild, moderate, and aggressive deficits — with caloric floor enforcement built in. Free, no signup required.
How a calorie deficit works
Fat loss requires eating fewer calories than you burn. One kilogram of body fat stores approximately 7,700 kcal of energy. A daily deficit of 500 kcal produces roughly 0.45 kg of fat loss per week — assuming the deficit comes primarily from fat stores rather than lean tissue.
The size of your deficit determines the speed of fat loss, but it also affects muscle retention, training performance, energy levels, hormonal function, and long-term adherence. Bigger is not always better — the goal is to lose fat while preserving as much muscle as possible.
Choosing the right deficit size
Mild deficit (15%)
A mild deficit of 300–450 kcal below maintenance is the most sustainable approach. It produces 0.3–0.5 kg of fat loss per week with excellent muscle preservation, minimal impact on training performance, and high adherence rates. This is the recommended starting point for most people.
Moderate deficit (20%)
A moderate deficit produces 0.5–0.7 kg of fat loss per week. At this level, protein intake becomes critical — 2.0–2.4 g/kg is necessary to protect lean mass. Training performance may dip on low-carb days, and recovery between sessions takes longer.
Aggressive deficit (25%)
Aggressive deficits should be used short-term only — 4 to 6 weeks maximum. Muscle loss risk increases substantially, hormonal adaptations accelerate, and adherence drops. Protein intake of 2.3–2.7 g/kg becomes essential to mitigate lean mass loss. Mettler et al. (2010) demonstrated that high protein intake during aggressive energy restriction preserved significantly more lean body mass compared to moderate protein intake.
Mettler, S et al. (2010). Increased protein intake reduces lean body mass loss during weight loss in athletes. Medicine & Science in Sports & Exercise, 42(2), 326–337.
Caloric floors and safety
This calculator enforces hard caloric minimums: 1,000 kcal/day for women and 1,200 kcal/day for men. Intake below these levels risks micronutrient deficiency, accelerated muscle loss, metabolic adaptation, and hormonal disruption. These are safety limits, not preferences — they cannot be overridden.
Why your deficit should change as you lose weight
Your TDEE decreases as your weight decreases. A 20% deficit at 85kg may shrink to an effective 10% deficit at 78kg if your calorie target is never recalculated. This is the most common reason fat loss stalls — the deficit quietly disappears.
Metabolic adaptation compounds this further. Trexler et al. (2014) documented reductions in energy expenditure of up to 400 kcal/day beyond what weight loss alone would predict. Your body actively downregulates non-exercise activity, reduces the thermic effect of food, and improves muscular efficiency — all working against your deficit. The only solution is to recalculate regularly from actual data.
Trexler, ET et al. (2014). Metabolic adaptation to weight loss: implications for the athlete. Journal of the International Society of Sports Nutrition, 11(1), 7.
Want a deficit that adjusts automatically?
Evid recalculates your TDEE and deficit every week based on your actual intake and weight data. Your calorie target stays accurate — even as your body changes.
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