Calorie Deficit Calculator
See exactly how many calories to eat per day and how long it will take to reach your target weight. Compare 10 different deficit levels side by side.
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Explore HubFit →How to Use This Calorie Deficit Calculator
Enter your age, sex, height, current weight, and target weight, then select your activity level. The calculator computes your TDEE using the Mifflin-St Jeor equation and generates a comparison table showing 10 different daily deficit scenarios, from a mild 100-calorie deficit to an aggressive 1,000-calorie deficit. For each scenario, you can see how many calories you should eat per day, how much weight you will lose per week and per month, how long it will take to reach your goal, and the estimated completion date.
What is a Calorie Deficit?
A calorie deficit occurs when you consume fewer calories than your body burns. This forces your body to tap into stored energy (primarily fat) to make up the difference. One kilogram of body fat contains approximately 7,700 calories, so a daily deficit of 500 calories leads to roughly 0.45 kg (1 lb) of fat loss per week. The size of your deficit determines how quickly you lose weight, but also affects how sustainable the diet feels and how much muscle you retain.
How Big Should Your Deficit Be?
For most people, a deficit of 300 to 500 calories per day is the sweet spot. This produces steady, sustainable fat loss of 0.3 to 0.5 kg per week while preserving muscle mass and keeping energy levels high. Larger deficits (600 to 1,000 calories) accelerate weight loss but come with trade-offs: increased hunger, greater risk of muscle loss, lower energy, and a higher likelihood of metabolic adaptation. The best deficit is one you can maintain consistently for weeks and months, not just days.
Why Extreme Deficits Backfire
When you cut calories too aggressively, your body responds by reducing non-exercise activity thermogenesis (NEAT), lowering thyroid output, and increasing hunger hormones like ghrelin. This metabolic adaptation can slow your weight loss to a crawl, even though you are eating very little. Extreme deficits also increase cortisol levels, which promotes water retention and makes the scale unreliable. A moderate deficit avoids these issues and produces more consistent, linear results.
The Role of Protein During a Deficit
Protein is your most important macronutrient during a calorie deficit. It preserves lean muscle mass, keeps you feeling full for longer, and has the highest thermic effect of food (your body burns more calories digesting protein than carbs or fat). Aim for 1.6 to 2.2 grams of protein per kilogram of bodyweight per day during a deficit. This is higher than general health recommendations, but research consistently shows it leads to better body composition outcomes during weight loss.
Adjusting Your Deficit Over Time
As you lose weight, your TDEE decreases because your body needs less energy to maintain a smaller frame. This means the same calorie intake that created a 500-calorie deficit at 90 kg might only create a 300-calorie deficit at 80 kg. Recalculate your numbers for every 5 to 10 lbs (2 to 5 kg) lost to keep your deficit on target. If weight loss stalls for more than 2 weeks, either reduce calories by 100 to 200 or increase your activity level slightly.
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