A calorie deficit occurs when energy expended exceeds energy consumed. This deficit compels the body to catabolize stored adipose tissue (body fat) and glycogen reserves to meet baseline metabolic demands.
deficit
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What Is deficit?
How to Calculate — The Thermodynamic 3,500 kcal/lb Rule Formula
We establish maintenance calories via the Mifflin-St Jeor equation multiplied by your PAL factor, subtracting 500 kcal/day for ~1 lb (0.45 kg) per week fat loss or 250 kcal/day for ~0.5 lb per week.
- Input your current weight, height, age, and weekly physical activity level.
- Select your target fat loss rate (e.g. 0.5 lb or 1.0 lb per week).
- Follow your personalized caloric intake goal and monitor weekly weight trends.
What Does Your Result Mean?
Frequently Asked Questions
What is the ideal calorie deficit for fat loss without muscle loss?
A moderate deficit of 300 to 500 kcal per day (15–20% below maintenance) represents the gold standard. It produces steady fat reduction while safeguarding metabolic rate and skeletal muscle tissue.
How many calories are in one pound of body fat?
One pound of adipose tissue contains approximately 3,500 kcal of stored chemical energy. A daily 500 kcal deficit yields an aggregate 3,500 kcal deficit across seven days, yielding ~1 lb fat loss.
What is the lowest safe daily calorie intake?
Clinical guidelines advise against unmonitored intakes below 1,200 kcal/day for women and 1,500 kcal/day for men. Extreme restriction precipitates hormonal dysfunction, micronutrient deficiencies, and muscle loss.
Why is my weight not dropping on a 500-calorie deficit?
Common causes include unmeasured liquid calories, sodium-induced water retention, elevated cortisol holding intramuscular fluid, or miscalculating baseline activity levels.
Does metabolic damage happen during a calorie deficit?
Permanent metabolic damage does not occur, but adaptive thermogenesis naturally lowers BMR by 5–15% as body mass decreases and NEAT downregulates to conserve energy.
What should my protein intake be during a calorie deficit?
Aim for 1.8 to 2.4 grams of protein per kilogram of body weight (0.8–1.1 g/lb) to preserve lean body mass and leverage higher thermic effect of food (TEF).
Should I use diet breaks or refeeds during fat loss?
Periodic 1–2 day refeeds at maintenance calories or a 1-week diet break every 6–8 weeks restores leptin levels, mitigates mental diet fatigue, and prevents training stagnation.
How does cardio compare to diet for creating a deficit?
Nutrition is vastly more efficient for establishing a deficit: cutting 500 kcal takes minutes of meal planning, whereas burning 500 kcal requires 45–60 minutes of vigorous cardiovascular effort.
Can you build muscle while in a calorie deficit?
Yes, known as body recomposition. It is readily achievable in beginners, individuals returning from a layoff, or individuals with higher starting body fat percentages who prioritize high protein and resistance training.
How long should a calorie deficit diet last?
Continuous deficits are best kept to 8 to 16 weeks at a time. After reaching a weight milestone, transition to 2–4 weeks at maintenance to normalize metabolic hormones before cutting again.
Next Steps
Now that you have your deficit result, use these tools to build a complete picture of your health metrics.
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Evidence-informed calculator · Updated August 2026
This calculator uses the stated published equation (Thermodynamic 3,500 kcal/lb Rule) and is for educational use. A calculator result is an estimate, not medical advice or an individual clinical assessment.
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