Calorie Deficit Calculator
Find your daily calorie target for fat loss — with a safe deficit based on your TDEE, goal weight, and timeline. Includes a muscle-loss risk warning for aggressive deficits.
(maintenance)
(kcal)
to goal
Deficit assessment
What is a calorie deficit and how does it work?
A calorie deficit occurs when you consume fewer calories than your body burns in a day. Your body must then draw on stored energy — primarily body fat — to make up the difference. Over time, this produces fat loss.
Your Total Daily Energy Expenditure (TDEE) is the total number of calories your body burns in a day, accounting for your Basal Metabolic Rate (BMR — calories burned at rest) plus all physical activity. Eating below your TDEE creates a deficit; the size of the deficit determines how quickly you lose fat.
The 3,500 calorie rule
A commonly cited figure is that 1 pound (0.45kg) of fat contains approximately 3,500 calories. A daily deficit of 500 kcal creates a weekly deficit of 3,500 kcal — roughly 0.45kg of fat loss per week. While useful as a rough guide, actual fat loss is more variable due to metabolic adaptation, water retention, and individual differences.
How big should your deficit be?
| Deficit size | Weekly loss | Assessment |
|---|---|---|
| ~250 kcal/day | ~0.25 kg | Very gentle — minimal muscle risk, very sustainable |
| ~500 kcal/day | ~0.5 kg | Recommended — sustainable, low muscle risk |
| ~750 kcal/day | ~0.75 kg | Moderate — requires higher protein to protect muscle |
| ~1000 kcal/day | ~1.0 kg | Aggressive — elevated muscle loss risk, harder to sustain |
📌 Why bigger deficits aren't always better
Larger deficits lose weight faster but increase the proportion coming from muscle rather than fat. Losing muscle reduces your metabolic rate, making future fat loss harder. A moderate deficit with high protein and resistance training produces better long-term body composition than an aggressive deficit without these safeguards.
Why protein matters during a deficit
When calories are restricted, your body can use muscle protein as an energy source — particularly if protein intake is low. Eating 1.6–2.4g of protein per kg of body weight during a deficit provides abundant amino acids, significantly reducing muscle breakdown. High protein intake also increases satiety and has a higher thermic effect than carbohydrates or fat — both useful during a deficit.
Metabolic adaptation: why deficits work less over time
As you lose weight, your TDEE decreases for two reasons: you are lighter (requiring less energy to move), and your body may reduce metabolic rate as a protective response to calorie restriction. This is why weight loss often slows or stalls after several weeks — the same deficit that worked initially no longer creates the same shortfall.
Practical responses include: recalculating your TDEE at your new weight, taking a diet break (eating at maintenance for 1–2 weeks), increasing physical activity, or accepting a slower rate of loss as a sustainable long-term approach.
Tracking your intake accurately
Research consistently shows that people underestimate their calorie intake by 20–50%. Common sources of error include not weighing food (using volume measures instead), forgetting oils and cooking fats, not accounting for sauces and condiments, and underreporting snacks. Using a kitchen scale and a calorie tracking app (such as MyFitnessPal or Cronometer) for at least 2–4 weeks gives a much more accurate baseline than estimation alone.