Calorie Calculator
For informational purposes only. Consult a healthcare professional before making dietary changes.
For informational purposes only. Consult a registered dietitian or healthcare professional before making significant dietary changes.
What Are Calories?
A calorie (technically a kilocalorie, kcal) is a unit of energy. In the context of food and nutrition, calories measure the amount of energy food provides to the body. Your body uses this energy for everything from breathing and maintaining body temperature to running and thinking. When you consume more calories than your body burns, the surplus is stored as fat. When you burn more than you consume, your body draws on stored energy and you lose weight.
Understanding your personal calorie needs is the starting point for any evidence-based nutrition strategy, whether your goal is weight loss, muscle gain, athletic performance, or simply maintaining your current weight.
Mifflin-St Jeor Formula
The Mifflin-St Jeor equation, developed in 1990, is the most widely validated formula for estimating Basal Metabolic Rate (BMR) and is recommended by the Academy of Nutrition and Dietetics as the preferred method for estimating calorie needs.
For Men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5
For Women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161
The constant at the end (+5 for men, -161 for women) accounts for the average metabolic difference between sexes, largely explained by differences in muscle mass and body composition. Men typically have higher BMRs because they carry more muscle relative to body weight.
Worked Example
A 35-year-old woman weighing 65 kg and 165 cm tall, moderately active (activity multiplier 1.55):
Activity Level Multipliers
| Level | Multiplier | Description |
|---|---|---|
| Sedentary | 1.2 | Office job, minimal movement, no structured exercise |
| Lightly Active | 1.375 | Light exercise 1-3 days/week (walking, yoga) |
| Moderately Active | 1.55 | Moderate exercise 3-5 days/week (jogging, cycling) |
| Very Active | 1.725 | Hard training 6-7 days/week |
| Extra Active | 1.9 | Athlete-level training or physical labor job |
Calories for Weight Loss vs. Weight Gain
A deficit or surplus of 500 calories per day results in approximately 0.5 kg (about 1 lb) of fat loss or gain per week. This is a commonly used, moderate target that minimizes muscle loss during a deficit and minimizes fat gain during a surplus.
For weight loss, aim for a deficit of 300-500 calories per day. Deficits larger than 1,000 calories per day risk muscle loss, nutritional deficiencies, and metabolic adaptation (where your body slows down to compensate). Slow, consistent weight loss of 0.5-0.75 kg/week is generally the most sustainable approach.
For muscle gain, a modest surplus of 200-500 calories above maintenance is ideal for most people. Eating too far above maintenance leads to excessive fat gain without proportionally more muscle. Beginners to resistance training can often gain muscle even at maintenance calories due to the "newbie gains" effect.
Macronutrient Calories
Once you know your target calories, you can plan your macronutrient (protein, carbohydrate, fat) intake. Each macro has a defined caloric density:
| Macronutrient | Calories per gram |
|---|---|
| Protein | 4 kcal/g |
| Carbohydrates | 4 kcal/g |
| Fat | 9 kcal/g |
| Alcohol | 7 kcal/g |
A common starting point is to allocate 30% of calories to protein, 40% to carbohydrates, and 30% to fat — but the optimal ratio varies based on individual goals, activity type, and personal tolerance. Use our Macro Calculator for a tailored macronutrient breakdown.
Frequently Asked Questions
What is the difference between BMR and TDEE?
BMR (Basal Metabolic Rate) is the number of calories your body needs to maintain basic life functions at complete rest — breathing, circulation, cell repair, and organ function. TDEE (Total Daily Energy Expenditure) is your BMR multiplied by an activity factor that accounts for the calories you burn through movement and exercise. TDEE is the number you should use for dietary planning because it reflects your actual daily calorie burn.
How accurate is the Mifflin-St Jeor formula?
The Mifflin-St Jeor equation (1990) is considered the most accurate predictive formula for BMR in non-obese adults, with an average error of around 10%. Studies consistently show it outperforms the older Harris-Benedict equation for most people. However, individual variation means actual calorie needs can still differ by 200-400 calories. For precise measurement, indirect calorimetry (breath analysis) performed by a clinical dietitian is the gold standard.
How many calories should I cut to lose 1 kg per week?
One kilogram of body fat contains approximately 7,700 calories. To lose 1 kg per week, you need a weekly calorie deficit of 7,700 calories — about 1,100 calories per day. This is quite aggressive and not recommended for most people. A more sustainable target is 0.5 kg per week, requiring a deficit of around 550 calories per day. Combining a moderate dietary deficit with increased exercise is healthier and leads to better long-term outcomes than diet alone.
What activity multiplier should I use?
Use Sedentary (×1.2) if you have a desk job and rarely exercise. Use Lightly Active (×1.375) if you exercise 1-3 days per week with light workouts like walking or yoga. Use Moderately Active (×1.55) if you do structured exercise 3-5 days per week at moderate intensity. Use Very Active (×1.725) if you train hard 6-7 days per week. Use Extra Active (×1.9) only if you have a physically demanding job (construction, military training) on top of daily exercise. Most sedentary office workers overestimate their activity level — when in doubt, start one level lower.
Do calorie needs change with age?
Yes. The Mifflin-St Jeor formula includes age as a factor — every additional year of age reduces BMR by 5 calories. From age 30 to 60, a person's BMR can drop by 150 calories purely due to ageing. Additionally, most people naturally become less active as they age. The combination means calorie needs typically decline by 50-100 calories per decade after age 30. This is why maintaining or building muscle through resistance training is so important — muscle tissue burns more calories at rest than fat tissue.
Related Calculators
- BMR Calculator — Basal Metabolic Rate with Mifflin-St Jeor and Harris-Benedict comparison
- BMI Calculator — Body Mass Index with WHO categories
- Macro Calculator — Protein, carb, and fat targets based on your TDEE
- TDEE Calculator — Total Daily Energy Expenditure in detail