Calorie Deficit & Weight Loss Calculator
Estimate how much weight you'll lose over a set number of weeks from your daily calorie deficit and exercise. Based on the well-established rule that ~7,700 kcal equals roughly 1 kg of body fat.
Last updated: May 2026
Compare with similar
About this calculator
This calculator estimates fat loss from a sustained calorie deficit. Your daily deficit is your maintenance calories (the amount that keeps your weight stable) minus your target intake, plus any calories burned through added exercise. It multiplies that daily deficit by 7 to get a weekly deficit, by the number of weeks, and then divides the total energy deficit by 7,700 — the approximate number of kilocalories stored in one kilogram of body fat. In formula terms: weight loss (kg) = ((maintenance − target + exercise) × 7 × weeks) ÷ 7,700. The science behind it is the energy-balance principle: when you consistently consume less energy than you expend, your body draws on stored fat to make up the difference. The 7,700 kcal-per-kilogram figure (about 3,500 kcal per pound) is a long-standing approximation that works well for moderate deficits over weeks to months. Edge cases and caveats matter: very large deficits do not produce proportionally faster fat loss because the body adapts by lowering metabolism, and a portion of early weight change is water, not fat. The model also assumes maintenance calories stay constant, but they actually fall as you lose weight, so real loss tends to be a little slower than a linear projection — which is why a sustainable deficit of 500–750 kcal per day, yielding about 0.5–0.75 kg per week, is widely recommended. Treat the result as a guiding estimate, not a guarantee.
How to use
Example 1 — maintenance 2,200 kcal, eating 1,700, plus 200 kcal of daily exercise, over 12 weeks. Enter Maintenance Calories = 2200, Target Calories = 1700, Weeks = 12, Exercise Calories = 200. Daily deficit is 700 kcal; over 12 weeks that is 700 × 7 × 12 = 58,800 kcal, divided by 7,700 ≈ 7.64 kg. Verify: a 700 kcal/day deficit predicts about 0.64 kg per week, comfortably in the sustainable range. Example 2 — maintenance 2,500, eating 2,000, 300 kcal exercise, over 8 weeks. Enter 2500, 2000, 8, 300. Daily deficit is 800 kcal; total 800 × 7 × 8 = 44,800 kcal ÷ 7,700 ≈ 5.82 kg. Verify: an 800 kcal/day deficit yields roughly 0.73 kg per week, still sustainable, and the shorter timeframe produces less total loss than the first example despite the larger daily deficit.
Frequently asked questions
Is the 3,500 calories per pound rule accurate?
The rule that roughly 3,500 kcal (about 7,700 kcal per kilogram) equals one pound of fat is a useful approximation, but it is not perfectly precise. It tends to overestimate long-term loss because it assumes your metabolism stays constant, when in reality it falls as you lose weight and your body becomes more efficient. The rule works best for moderate deficits over a span of weeks to a few months. For very long or very aggressive diets, dynamic models that account for metabolic adaptation are more accurate. Treat the figure as a solid starting estimate that will likely run slightly optimistic over time.
How fast is it safe to lose weight?
Most health authorities recommend losing about 0.5 to 1 kg (1 to 2 pounds) per week, which corresponds to a daily deficit of roughly 500 to 1,000 kcal. This pace preserves more muscle, is easier to sustain, and reduces the risk of nutritional deficiencies and gallstones associated with very rapid loss. Larger deficits produce faster initial results but often backfire through muscle loss, fatigue, intense hunger, and rebound weight gain. Going below about 1,200 kcal a day for women or 1,500 for men without medical supervision is generally discouraged. Slower, steady loss is far more likely to stick.
Why is my early weight loss faster than this predicts?
The first week or two of a diet usually shows a larger drop than the fat-loss math predicts, because much of it is water rather than fat. When you cut calories — especially carbohydrates — your body depletes its glycogen stores, and each gram of glycogen holds several grams of water, so the scale falls quickly at first. This water weight returns if you eat more carbs, which is why weight can fluctuate day to day. True fat loss is slower and steadier. Judge progress over several weeks rather than reacting to short-term swings, and use the same time and conditions when weighing yourself.
What is a common mistake when running a calorie deficit?
The most common mistake is underestimating calorie intake and overestimating calories burned, which shrinks the real deficit and stalls progress. People often forget liquid calories, cooking oils, and snacks, and they trust exercise-machine or tracker estimates that tend to inflate burn. Another error is cutting calories so aggressively that hunger and fatigue lead to bingeing and abandonment of the plan. Failing to adjust maintenance calories downward as you lose weight also causes a plateau. Accurate tracking, a moderate deficit, adequate protein, and periodic recalculation of your maintenance level address most of these pitfalls.
When should I NOT rely on this calculator?
This is an educational estimate, not medical or nutritional advice, and you should consult a doctor or registered dietitian before starting a significant diet, especially if you have a medical condition, are pregnant or breastfeeding, are under 18, or have a history of disordered eating. It assumes constant maintenance calories and a linear relationship that breaks down for very aggressive or very long diets due to metabolic adaptation. It does not distinguish fat from muscle or water, account for individual variation in metabolism, or guarantee results. It also cannot tell you whether your target intake is nutritionally adequate. Use it to set realistic expectations, and seek professional guidance for a personalized, safe plan.