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A calorie deficit occurs when you consume fewer calories than your body burns. It is the only proven mechanism for fat loss. A calorie deficit calculator helps you work out exactly how many calories to eat each day based on your TDEE and your desired rate of weight change.
The fundamental relationship is: 1 kg of body fat contains approximately 7,700 calories. To lose 0.5 kg per week, you need a daily deficit of 7,700 / 7 = 1,100 calories. To lose 0.5 kg per week more sustainably, aim for a 550 calorie daily deficit, which totals 3,850 calories per week. This principle is validated by decades of research compiled in a landmark New England Journal of Medicine calorie restriction study.
Deficit vs Surplus Planning
| Goal | Daily change | Weekly calories | Weekly weight change |
|---|---|---|---|
| Lose 0.25 kg/week | -275 cal | -1,925 cal | -0.25 kg |
| Lose 0.5 kg/week | -550 cal | -3,850 cal | -0.5 kg |
| Lose 1.0 kg/week | -1,100 cal | -7,700 cal | -1.0 kg |
| Gain 0.25 kg/week | +275 cal | +1,925 cal | +0.25 kg |
| Gain 0.5 kg/week | +550 cal | +3,850 cal | +0.5 kg |
Given that body weight also fluctuates with water retention, hormones, and food volume in the digestive system, measure your weight weekly rather than daily for an accurate trend. With that in mind, daily weighing adds noise that can be discouraging.
Finding Your TDEE
To use this calculator, you first need your TDEE. Use our BMR Calculator to figure out your TDEE from your weight, height, age, and activity level. If you have been maintaining weight on a known number of calories, that number is your real-world TDEE.
Alternatively, carry out a 2-week food log without changing your diet. If your weight is stable, average your daily calories to narrow down your maintenance level. This real-world TDEE is often more accurate than formula-based estimates because it accounts for individual metabolic variation.
Avoiding Muscle Loss
A deficit that is too large causes muscle breakdown alongside fat loss. Research from the International Journal of Sport Nutrition recommends keeping protein intake at 1.6-2.2 g per kg of body weight during a calorie deficit to preserve lean mass. On top of that, resistance training 2-3 times per week is the most effective way to build up a muscle-sparing signal even during a large deficit.
As a result, the optimal deficit for most people is 300-500 calories per day: enough to produce visible fat loss over weeks while preserving strength. Use our Macro Calculator to build up a protein-prioritized meal plan within your calorie target. The American Heart Association nutrition guidelines provide food quality context.