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What is a Calorie?

A calorie is a unit of energy. In nutrition, we actually measure kilocalories (kcal)—often just called "calories." When food labels say a serving has 200 calories, they mean 200 kilocalories of energy. Your body uses this energy for everything from breathing and thinking to walking and exercising. Understanding your calorie needs is fundamental to weight management and overall health.

BMR vs TDEE: Key Terms Explained

• BMR (Basal Metabolic Rate): The calories your body burns at complete rest—just to keep your heart beating, lungs breathing, and organs functioning. This typically accounts for 60-75% of daily calorie expenditure.
• TDEE (Total Daily Energy Expenditure): Your total daily calories burned, including BMR plus all physical activity and digestion. This is the number you need for weight management.
• NEAT: Non-Exercise Activity Thermogenesis—calories burned through daily movements like walking, fidgeting, and standing.
• TEF: Thermic Effect of Food—calories burned digesting food (about 10% of intake).

The Mifflin-St Jeor Formula

We use the Mifflin-St Jeor equation (1990), considered the most accurate BMR formula for most adults:

Men: BMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age) + 5

Women: BMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age) - 161

TDEE is then calculated by multiplying BMR by an activity factor (1.2-1.9).

Real-World Calorie Examples

• 30-year-old man, 5'9", 165 lbs, moderate activity: BMR ~1,730, TDEE ~2,680 calories
• 25-year-old woman, 5'5", 140 lbs, light activity: BMR ~1,430, TDEE ~1,965 calories
• 45-year-old man, 6'0", 200 lbs, sedentary: BMR ~1,850, TDEE ~2,220 calories
• 35-year-old woman, 5'6", 160 lbs, very active: BMR ~1,480, TDEE ~2,550 calories
• 50-year-old man, 5'10", 185 lbs, active: BMR ~1,720, TDEE ~2,665 calories

Activity Level Multipliers

• Sedentary (1.2): Desk job, little to no exercise
• Lightly Active (1.375): Light exercise 1-3 days/week
• Moderately Active (1.55): Moderate exercise 3-5 days/week
• Very Active (1.725): Hard exercise 6-7 days/week
• Extra Active (1.9): Very hard exercise, physical job, or training twice/day

Calories for Weight Goals

The basic principle: calories in vs. calories out. One pound of body fat equals approximately 3,500 calories.

• To lose 1 lb/week: Eat 500 calories below your TDEE daily (500 × 7 = 3,500)
• To lose 2 lbs/week: Eat 1,000 calories below TDEE (maximum recommended deficit)
• To maintain weight: Eat at your TDEE
• To gain 1 lb/week: Eat 500 calories above TDEE (for muscle building, combine with resistance training)

Macronutrient Breakdown

Calories come from three macronutrients:

• Protein: 4 calories per gram. Essential for muscle preservation and satiety. Aim for 0.7-1g per pound of body weight when active.
• Carbohydrates: 4 calories per gram. Primary energy source for exercise and brain function.
• Fat: 9 calories per gram. Essential for hormones, nutrient absorption, and satiety. Don't go below 20% of total calories.

Common Macro Splits

• Balanced (30/40/30): 30% protein, 40% carbs, 30% fat—good for general health
• Low Carb (40/20/40): 40% protein, 20% carbs, 40% fat—may help with appetite control
• High Protein (40/35/25): Best for muscle building and preservation during weight loss
• Keto (25/5/70): Very low carb, high fat—induces ketosis for some benefits but difficult to sustain

Safe Calorie Limits

• Minimum for women: 1,200 calories/day (unless medically supervised)
• Minimum for men: 1,500 calories/day (unless medically supervised)
• Maximum deficit: 1,000 calories below TDEE (2 lbs/week loss)
• Very low calorie diets (VLCDs): Below 800 calories—require medical supervision

Related Health Tools

• BMI Calculator – Check if your weight is in a healthy range
• Body Fat Calculator – Estimate your body composition
• Macro Calculator – Get detailed protein, carb, and fat targets

About Our Calculations

Our calorie calculator uses the Mifflin-St Jeor equation (1990), which studies have shown to be the most accurate for estimating resting metabolic rate in most adults (±10% accuracy). Individual metabolism varies based on genetics, body composition, hormones, and other factors. Use these results as a starting point and adjust based on your actual results over 2-4 weeks. For medical conditions affecting metabolism (thyroid disorders, diabetes, etc.), consult a healthcare provider.