How many calories to lose 1 kg of fat?

1 kg of body fat corresponds to approximately 7,700 kcal. With a deficit of 500 kcal/day, you will theoretically lose 1 kg in 15 days (500 × 15 ≈ 7,500 kcal). In practice, loss varies depending on your metabolism, water retention, muscle mass and physical activity level.

What calorie deficit is recommended for weight loss?

A deficit of 300–500 kcal/day is the standard recommended by nutritionists and dietitians. It allows for a loss of 0.25–0.5 kg per week — progressive, sustainable, and without significant risk of muscle loss. Too large a deficit (> 750 kcal) increases the risk of deficiencies, muscle catabolism and yo-yo effect upon stopping.

How do you calculate your basal metabolic rate (BMR)?

Our calculator uses the Mifflin-St Jeor formula, considered the most accurate by current scientific literature. For men: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5. For women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161. BMR represents the minimum calorie needs at complete rest (vital functions only).

What's the difference between BMR and TDEE?

BMR (Basal Metabolic Rate) is the energy spent at complete rest to maintain vital functions: breathing, blood circulation, temperature regulation. TDEE (Total Daily Energy Expenditure) also includes the energy spent during your daily physical activities. The deficit is applied to the TDEE to calculate your calorie goal.

How much protein to eat in a calorie deficit?

In a calorie deficit, it's recommended to consume between 1.8 and 2.5 g of protein per kg of body weight — compared to 0.8 g/kg normally. High protein intake preserves muscle mass, increases satiety and benefits from higher dietary thermogenesis (protein 'costs' more energy to digest). Our calculator suggests 2.2 g/kg as the optimal target.

Is it dangerous to reduce calories too much?

Yes. Below 1,200 kcal/day for women and 1,500 kcal/day for men, you expose your body to serious risks: vitamin and mineral deficiencies, accelerated muscle loss, chronic fatigue, hormonal disorders and metabolic slowdown. Our tool automatically warns you if your deficit exceeds these critical thresholds.

Do you need to exercise to lose weight?

No, it's not mandatory. Weight loss is determined approximately 80% by diet and 20% by physical activity. It's entirely possible to create a calorie deficit solely by adjusting your intake. However, exercise — particularly strength training — improves body composition, preserves muscle mass in a deficit and makes weight maintenance easier long-term.

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Calorie deficit calculator

Q: What is a calorie deficit?

A calorie deficit occurs when you consume fewer calories than your body expends in a day. It's the only proven physiological mechanism for losing body fat: when your intake is lower than your expenditure, your body draws on its fat reserves to make up the difference. The size of the deficit directly determines the speed of weight loss.

Obtenez en quelques secondes votre basal metabolic rate (BMR), votre total daily energy expenditure (TDEE) et votre daily calorie goal pour perdre du poids efficacement.

Your information

Sex

Age

yrs

Height

Weight

Target weight (optional)

Used to estimate when you'll reach your goal.

Activity level

Weight loss pace

per week0,45 kg−500 kcal / day

MildAggressive

A deficit of 300–500 kcal/day is recommended for sustainable loss while preserving muscle mass.

Enter your age, height and weight

to get your personalized calorie goal

How does the calculation work?

Step 01

Basal Metabolic Rate (BMR)

We calculate your minimum calorie needs at rest using the Mifflin-St Jeor formula — the most accurate, based on your sex, age, height and weight.

Step 02

Total Daily Energy Expenditure (TDEE)

We multiply your BMR by a physical activity coefficient to get your actual daily calorie expenditure: this is your maintenance threshold.

Step 03

Calorie goal & macros

We subtract your chosen deficit from the TDEE to get your calorie target, then calculate the optimal breakdown of protein, carbs and fat.

What is a calorie deficit?

A calorie deficit is the fundamental principle of any weight loss. It occurs when your daily calorie intake is lower than your total daily energy expenditure (TDEE). To create this deficit, you can reduce your food intake, increase your physical activity, or combine both approaches — the combination being generally the most effective and sustainable.

For example, if your TDEE is 2,200 kcal/day and you consume 1,700 kcal, you are in a 500 kcal deficit. Over a week, that represents 3,500 kcal — approximately 0.5 kg of fat lost, since 1 kg of fat ≈ 7,700 kcal.

The Mifflin-St Jeor formula: why is it the most accurate?

Several formulas exist to estimate basal metabolic rate: Harris-Benedict (1919), Katch-McArdle, and Mifflin-St Jeor (1990). The latter is recognized as the most accurate for the general population by numerous meta-analyses, notably because it was developed and validated on a modern sedentary population, more representative of current reality.

Mifflin-St Jeor formula:

Male: BMR = (10 × weight) + (6.25 × height) − (5 × age) + 5

Female: BMR = (10 × weight) + (6.25 × height) − (5 × age) − 161

weight in kg · height in cm · age in years

Physical activity coefficients (PAL)

The TDEE is obtained by multiplying the BMR by an activity factor (PAL — Physical Activity Level) that reflects your daily physical expenditure. This coefficient is the main source of inaccuracy in calculators: be honest in your assessment for a reliable result.

Level	Description	Multiplier
🪑 Sedentary	Office work, little or no exercise	×1.2
🚶 Lightly active	Light exercise 1–3 days/week	×1.375
🏃 Moderately active	Regular exercise 3–5 days/week	×1.55
🏋️ Very active	Intense exercise 6–7 days/week	×1.725
⚡ Extremely active	Elite athlete or physical job	×1.9

Which calorie deficit should you choose?

There is no universal answer — it all depends on your starting point, your tolerance to restriction and your goals. Here is a comparison of the main approaches:

Gentle loss−250 kcal/jour

✓ Pros

• Very sustainable long-term
• Minimal risk of muscle loss
• Easy to maintain without frustration

✗ Cons

• Slow progress (~0.25 kg/wk)
• Results barely visible short-term

Moderate loss−500 kcal/jour

⭐ Ideal

✓ Pros

• Optimal effectiveness/sustainability balance
• Standard recommended by nutritionists
• ~0.5 kg loss per week

✗ Cons

• May require an adaptation period

Fast loss−750 kcal/jour

✓ Pros

• Accelerated loss (~0.75 kg/wk)
• Suited to significantly overweight people

✗ Cons

• Increased risk of muscle loss
• Possible fatigue and cravings
• Hard to sustain long-term

Aggressive loss−1 000 kcal/jour

✓ Pros

• Rapid loss (~1 kg/wk)

✗ Cons

• High risk of nutritional deficiencies
• Significant muscle loss
• Metabolic slowdown
• Should only be done under medical supervision

4 tips to stick to your calorie deficit

Prioritize protein

Aiming for 1.8–2.5 g/kg of body weight preserves muscle mass, increases satiety and generates higher dietary thermogenesis — protein is your best ally in a deficit.

Track your intake

Using a calorie tracking app (like Micron) is the most effective way to stay within your goal. We tend to overestimate expenditure and underestimate intake without a measuring tool.

Add strength training

Resistance training during a deficit preserves and builds muscle mass, improving body composition and keeping your metabolism active — avoiding metabolic slowdown.

Sleep enough

Lack of sleep disrupts hunger hormones (ghrelin and leptin) and increases cravings, particularly for sweet and fatty foods. 7–9 hours per night optimizes fat loss.

Frequently asked questions about calorie deficit

Pour aller plus loin

Guide

Déficit calorique

Comment construire un déficit qui dure : leviers, spécificités femmes/sportifs, plateau et erreurs à éviter.

Lire →

Calculateur

Surplus calorique

Calculez votre surplus pour la prise de masse — lean bulk, projection muscle/gras sur 12 semaines.

Lire →

Guide

Recomposition corporelle

Perdre du gras et gagner du muscle simultanément : pour qui ça marche, protocole, mini-quiz d'éligibilité.

Lire →

Hub

Carences en vitamines

Identifier et corriger les carences en vitamines et minéraux les plus fréquentes.

Lire →

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