Calorie Deficit Calculator
Work out exactly how many calories to eat each day to lose weight at a safe, steady pace.
This calculator estimates your maintenance calories (TDEE) using the Mifflin-St Jeor equation and applies a deficit based on your chosen pace. Calorie targets are capped at recognised safe minimums. This is a general estimate for healthy adults — speak with a doctor or registered dietitian before starting any calorie-restricted plan, especially if you have a history of disordered eating, are pregnant, or have a medical condition.
What is a Calorie Deficit?
A calorie deficit occurs when you consume fewer calories than your body expends over a given period. Since your body requires energy to sustain all biological functions and physical activity, a shortage of incoming calories forces it to draw on stored energy — primarily body fat — to make up the difference. This process of accessing stored fat for fuel is the biological mechanism behind all fat loss, regardless of the specific diet approach used.
The fundamental principle of energy balance — often summarised as "calories in vs calories out" — underpins every successful weight loss strategy. While the quality and composition of your diet matters significantly for health, hunger management, and performance, the calorie deficit remains the non-negotiable driver of fat loss.
How to Use This Calorie Deficit Calculator
Select your gender, enter your age, height, current weight, and activity level. Then choose your desired weekly weight loss pace. The calculator instantly shows your maintenance calories (TDEE), your safe daily calorie target, the exact deficit, projected weekly and 12-week weight loss, and a safety check — the target is automatically capped at generally recognised safe minimums to prevent muscle loss and metabolic harm.
How Much Deficit is Safe and Effective?
| Weekly Loss Pace | Daily Deficit | Best For |
|---|---|---|
| 0.25 kg/week | ~275 kcal/day | Maintenance, athletes, beginners |
| 0.5 kg/week | ~550 kcal/day | Recommended for most people |
| 0.75 kg/week | ~820 kcal/day | Faster progress, higher protein needed |
| 1.0 kg/week | ~1,100 kcal/day | Maximum — requires medical monitoring |
Research consistently shows that a deficit of 500 calories per day — producing approximately 0.5kg of fat loss per week — is the sweet spot for preserving lean muscle mass while losing fat at a meaningful pace. Faster deficits accelerate muscle loss and metabolic adaptation.
Why 3,500 Calories Does Not Equal Exactly 0.5kg of Fat
The traditional "3,500 calorie deficit = 1 pound of fat" rule is a useful simplification but not perfectly accurate. In reality, as you lose weight, your body adapts by reducing metabolic rate (adaptive thermogenesis), reducing spontaneous physical activity (NEAT), and increasing appetite. This means the actual weight loss from a given deficit diminishes over time — a phenomenon known as metabolic adaptation. Our calculator uses the standard 7,700 kcal/kg approximation as a practical guide, understanding that real-world results will vary and require periodic recalibration.
The Role of Protein in a Calorie Deficit
During a calorie deficit, your body does not exclusively burn fat — it also breaks down muscle tissue for energy unless protein intake is sufficiently high. Research shows that consuming 1.8–2.4g of protein per kg of bodyweight during a deficit significantly reduces muscle loss compared to lower intakes. This is why high protein is the most important dietary strategy during fat loss — not just for muscle preservation, but also because protein is the most satiating macronutrient, making the deficit easier to sustain.
Use our Protein Intake Calculator alongside your calorie deficit to ensure you are protecting your muscle mass throughout the process.
Safe Minimum Calorie Thresholds
Our calculator automatically prevents your calorie target from dropping below generally recognised safe minimums:
- Men: 1,500 kcal/day minimum
- Women: 1,200 kcal/day minimum
Eating below these thresholds for extended periods risks muscle loss, nutrient deficiencies, hormonal disruption, reduced bone density, and metabolic adaptation that makes future weight management significantly harder. If your goal requires a larger deficit than these floors allow, consult a registered dietitian for supervised guidance.
When to Recalculate Your Deficit
Your maintenance calories (TDEE) decrease as your weight decreases — a lighter body burns fewer calories. This is why progress often stalls after 6–8 weeks without a recalculation. Recalculate your TDEE and this calculator every 4–6 weeks, or whenever your weight changes by more than 3–4kg, to ensure your deficit remains accurate and effective.
Frequently Asked Questions
Related Calculators
Sources
- Hall KD, et al. Quantification of the effect of energy imbalance on bodyweight. The Lancet. 2011;378(9793):826-837.
- Helms ER, et al. A systematic review of dietary protein during caloric restriction in resistance trained lean athletes. JISSN. 2014;11:20.
- Trexler ET, et al. Metabolic adaptation to weight loss: implications for the athlete. JISSN. 2014;11(1):7.