Formula & Methodology
This calculator supports four clinically validated BMR formulas. Your BMR is then multiplied by an activity factor to produce your TDEE (Total Daily Energy Expenditure).
Mifflin-St Jeor (Default)
BMR (male) = (10 × weight_kg) + (6.25 × height_cm) − (5 × age) + 5 BMR (female) = (10 × weight_kg) + (6.25 × height_cm) − (5 × age) − 161 Harris-Benedict (Revised 1984)
BMR (male) = (13.397 × weight_kg) + (4.799 × height_cm) − (5.677 × age) + 88.362 BMR (female) = (9.247 × weight_kg) + (3.098 × height_cm) − (4.330 × age) + 447.593 Katch-McArdle
BMR = 370 + (21.6 × lean_body_mass_kg) Requires body fat % input. Most accurate for individuals who know their body composition.
Activity Multipliers
Sedentary: ×1.2 | Light: ×1.375 | Moderate: ×1.55 | Active: ×1.725 | Athlete: ×1.9 Key Terms
- BMR
- Basal Metabolic Rate — the minimum calories your body burns at complete rest to maintain vital organ function.
- TDEE
- Total Daily Energy Expenditure — your BMR multiplied by an activity factor. This is your true maintenance calorie number.
- Caloric Deficit
- Eating fewer calories than your TDEE, causing your body to burn stored energy (fat) for the shortfall.
- Macronutrients
- The three energy-providing nutrients: protein (4 kcal/g), carbohydrates (4 kcal/g), and fats (9 kcal/g).
- Body Recomposition
- Simultaneously losing fat and building muscle by eating at maintenance with high protein and resistance training.
- TEF
- Thermic Effect of Food — the energy cost of digesting food, approximately 10% of total calorie intake.
- Metabolic Adaptation
- The body's tendency to reduce energy expenditure during prolonged calorie restriction, causing weight loss plateaus.
Worked Examples
Example 1 — Woman on a Moderate Cut
Profile: 28-year-old female, 165 cm, 68 kg, moderate activity, Mifflin-St Jeor
BMR = (10 × 68) + (6.25 × 165) − (5 × 28) − 161 = 680 + 1031.25 − 140 − 161 = 1,410 kcal
TDEE = 1,410 × 1.55 = 2,186 kcal
Moderate deficit (−500 kcal) → Daily Target = 1,686 kcal → ~0.45 kg/week loss
Example 2 — Man Lean Bulking
Profile: 32-year-old male, 180 cm, 82 kg, very active, Harris-Benedict
BMR = (13.397 × 82) + (4.799 × 180) − (5.677 × 32) + 88.362 = 1,098.55 + 863.82 − 181.66 + 88.362 = 1,869 kcal
TDEE = 1,869 × 1.725 = 3,224 kcal
Lean bulk (+250 kcal) → Daily Target = 3,474 kcal → ~0.23 kg/week gain
Example 3 — Athlete Using Katch-McArdle
Profile: 25-year-old male, 78 kg, 12% body fat, athlete level
Lean Mass = 78 × (1 − 0.12) = 68.64 kg
BMR = 370 + (21.6 × 68.64) = 370 + 1,482.6 = 1,853 kcal
TDEE = 1,853 × 1.9 = 3,520 kcal → maintaining at athlete level activity
BMR Formula Comparison
| Formula | Best For | Requires Body Fat? | Accuracy | Notes |
|---|---|---|---|---|
| Mifflin-St Jeor | General population | No | ±10% | Clinical gold standard since 2005 |
| Harris-Benedict | Clinical settings | No | ±12% | Revised 1984 version; slightly overestimates |
| Katch-McArdle | Lean/athletic individuals | Yes | ±5–8% | Most accurate when body fat is known |
| Oxford (2005) | Diverse populations | No | ±10% | Best validated across ethnicities and age groups |
Understanding Your Daily Calorie Needs
Calories are the fundamental unit of energy your body uses to power everything from breathing and digestion to running and lifting weights. Understanding how many calories you need each day is the cornerstone of any nutrition plan, whether your goal is weight loss, muscle gain, or simply maintaining a healthy body composition.
How Your Body Burns Calories
Your total daily energy expenditure consists of three components. Basal metabolic rate accounts for roughly 60–70% of your daily burn and covers involuntary functions like heartbeat, breathing, and cell repair. The thermic effect of food uses about 10% of your intake to digest and absorb nutrients. Physical activity — both structured exercise and daily movement — makes up the remaining 20–30%. This is why your activity level selection matters so much when calculating calorie targets.
Choosing the Right BMR Formula
The Mifflin-St Jeor equation is the default because the American Dietetic Association identified it as the most reliable predictor of BMR for the general population. However, if you have a DEXA scan or reliable body fat measurement, the Katch-McArdle formula can be significantly more accurate because it calculates energy needs based on lean mass rather than total body weight. This makes a meaningful difference for muscular individuals whose weight-based BMR estimates may be artificially high.
The Science of Calorie Deficits
A pound of body fat stores approximately 3,500 calories of energy. A daily deficit of 500 calories theoretically produces one pound of fat loss per week. In practice, the rate slows over time due to metabolic adaptation — your body becomes more efficient and burns fewer calories as you lose weight. This is why periodic recalculation and diet breaks are recommended strategies for sustained progress.
Macro Splits and Performance
While total calories determine whether you gain or lose weight, macronutrient ratios influence body composition and performance. Higher protein intakes (1.6–2.2 g/kg) during a deficit preserve lean muscle mass. Adequate carbohydrates fuel high-intensity training. Dietary fats support hormone production and nutrient absorption. The preset macro splits in this calculator provide evidence-based starting points that you can customize to fit your preferences and goals.
When to Recalculate
Your calorie needs are not static. Recalculate your targets whenever your weight changes by 5% or more, when your activity level shifts significantly, or every 4–6 weeks during an active cut or bulk phase. The scenario comparison table built into this calculator makes it easy to preview how different intensity levels will affect your timeline and daily targets.