SlothLab ToolsCalorie Calculator
Estimate your daily calorie needs using the Mifflin-St Jeor equation.
kg
cm
years
Your Daily Calories
BMR
1618 kcal
Calories at complete rest
TDEE
2507 kcal
Daily calorie needs
Weight Loss
2007
kcal/day
Maintain
2507
kcal/day
Weight Gain
3007
kcal/day
Based on the Mifflin-St Jeor equation (1990). Weight loss/gain targets assume ±500 kcal/day (~0.45 kg/week).
BMR vs TDEE
BMR: 1618 kcal (65%)+889 kcal activity
Macro Breakdown
Protein
188g
30% · 4 kcal/g
Carbs
251g
40% · 4 kcal/g
Fat
84g
30% · 9 kcal/g
Last Updated: March 16, 2026
⚠ This calculator provides general estimates based on the Mifflin-St Jeor equation. Individual calorie needs vary based on metabolism, health conditions, and other factors. Consult a registered dietitian or healthcare provider before making significant dietary changes.
How It Works
This calculator uses the Mifflin-St Jeor equation, published in 1990 in the American Journal of Clinical Nutrition and widely considered the most accurate predictive equation for basal metabolic rate (BMR) in healthy adults. BMR represents the calories your body burns at complete rest just to maintain vital functions like breathing, circulation, and cell production. The equation accounts for weight, height, age, and sex. For males: BMR = 10×weight(kg) + 6.25×height(cm) − 5×age + 5. For females: BMR = 10×weight(kg) + 6.25×height(cm) − 5×age − 161. Your BMR is then multiplied by a Physical Activity Level (PAL) factor ranging from 1.2 (sedentary) to 1.9 (extra active) to estimate your Total Daily Energy Expenditure (TDEE) — the total calories you need per day.
Why This Matters
Understanding your daily calorie needs is fundamental to virtually every nutrition and fitness goal — whether you are trying to lose weight, build muscle, maintain your current physique, or simply eat more mindfully. According to the CDC, over 70% of American adults are overweight or obese, and miscalculating calorie needs is a primary contributor. Many people dramatically underestimate their intake (studies show underreporting of 30–50%) or follow generic 2,000-calorie recommendations that may be hundreds of calories off from their actual needs.
The Mifflin-St Jeor equation provides a personalized starting point that accounts for your specific body metrics and activity level. Knowing your TDEE allows you to create precise, sustainable caloric deficits for weight loss (typically 500 kcal/day for 0.45 kg/week) or surpluses for muscle building (200–500 kcal/day). This data-driven approach is far more effective than guessing or following fad diets. Research consistently shows that people who track calories — even roughly — are more successful at achieving and maintaining their weight goals over the long term.
Real-World Examples
Scenario 1 — Office worker seeking weight loss: A 40-year-old sedentary woman (65 kg, 163 cm) has a BMR of 1,322 kcal and TDEE of 1,587 kcal. To lose 0.45 kg per week, she targets 1,087 kcal — but this falls below the 1,200 kcal minimum recommended without medical supervision. Her better strategy: increase activity to 'Lightly Active' (TDEE 1,818 kcal), allowing a safe 1,318 kcal target while still achieving her goal.
Scenario 2 — Athlete calculating training-day nutrition: A 28-year-old male competitive cyclist (78 kg, 180 cm, very active) has a TDEE of approximately 3,200 kcal. On race days with 4+ hours of riding, he may need 4,500–5,000 kcal. He uses the calculator's baseline TDEE and adds sport-specific calorie estimates to prevent under-fueling, which could impair recovery and performance.
Scenario 3 — New parent adjusting for lifestyle change: A 32-year-old man previously classified as 'Active' (TDEE 2,800 kcal) transitions to a sedentary desk job after having a child. His new TDEE drops to approximately 2,200 kcal. Without recalculating, he would overconsume by 600 kcal daily — enough to gain roughly 2.3 kg per month. The calculator helps him adjust intake proactively.
Methodology & Sources
This calculator uses the Mifflin-St Jeor equation (1990), widely considered the most accurate predictive equation for basal metabolic rate (BMR) in healthy adults. The formulas are: Males: BMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age in years) + 5. Females: BMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age in years) - 161.
Total Daily Energy Expenditure (TDEE) is calculated by multiplying BMR by a Physical Activity Level (PAL) factor: Sedentary (1.2), Lightly Active (1.375), Moderately Active (1.55), Very Active (1.725), Extra Active (1.9). These PAL factors were established by the WHO/FAO/UNU Expert Consultation on Human Energy Requirements (2004) and represent multipliers that account for the thermic effect of physical activity and non-exercise activity thermogenesis (NEAT).
Comparative methods: The Mifflin-St Jeor equation was validated against indirect calorimetry (the gold standard for measuring metabolic rate) and found to predict BMR within 10% for approximately 82% of individuals — outperforming the Harris-Benedict equation (1919), which overestimates BMR by 5–15% in modern populations due to secular trends in body composition. The Katch-McArdle formula offers improved accuracy for lean or muscular individuals by incorporating body fat percentage, but requires an additional measurement most users do not have. The Cunningham equation similarly uses lean body mass and is preferred in sports nutrition contexts.
Macronutrient breakdowns use evidence-based nutritional guidelines: Protein provides 4 kcal/g (recommended 10–35% of total calories per USDA), carbohydrates provide 4 kcal/g (45–65% of calories), and fat provides 9 kcal/g (20–35% of calories). Weight loss and gain targets use the widely accepted ±500 kcal/day adjustment, corresponding to approximately 0.45 kg (1 lb) per week based on the principle that 1 kg of body fat stores approximately 7,700 kcal.
Data sources: Mifflin MD, St Jeor ST, et al. 'A new predictive equation for resting energy expenditure in healthy individuals.' American Journal of Clinical Nutrition (1990); WHO/FAO/UNU Expert Consultation on Human Energy Requirements (2004); Frankenfield et al. 'Comparison of predictive equations for resting metabolic rate' (JADA, 2005).
Limitations: The equation is accurate within approximately 10% for most adults but may be less accurate for very muscular individuals (who have higher BMR per kg), the morbidly obese, the very elderly, or individuals with metabolic disorders such as hypothyroidism. Individual metabolic rate varies based on genetics, hormones (especially thyroid function), body composition, ambient temperature, and adaptive thermogenesis. The equation does not account for metabolic adaptation during prolonged caloric restriction, where BMR may decrease beyond what weight loss alone would predict.
Common Mistakes to Avoid
1. Choosing the wrong activity level: This is the most common error and can skew results by 300–600 calories. 'Moderately Active' means structured exercise 3–5 days per week, not just walking to the car. Most desk workers with occasional gym visits should select 'Lightly Active' or 'Sedentary.' Overestimating activity level leads to overeating and stalled weight loss.
2. Treating the calculator output as exact: The Mifflin-St Jeor equation predicts BMR within ±10% for most people, meaning your actual needs could be 150–300 calories higher or lower than calculated. Use the result as a starting point, then adjust based on real-world results over 2–4 weeks. If you are not losing or gaining weight as expected, adjust by 100–200 calories.
3. Creating too large a caloric deficit: Aggressive deficits (>1,000 kcal/day) trigger metabolic adaptation, where your body reduces BMR to conserve energy. This leads to plateaus, muscle loss, fatigue, and eventual rebound weight gain. The American College of Sports Medicine recommends no more than a 500–1,000 kcal daily deficit, and never consuming below 1,200 kcal (women) or 1,500 kcal (men) without medical supervision.
4. Ignoring the thermic effect of different macronutrients: Not all calories are metabolized equally. Protein requires 20–30% of its calories for digestion, while fat requires only 0–3%. Two diets with identical total calories but different macro ratios can produce different body composition outcomes. Pay attention to the macro breakdown, especially protein intake during weight loss to preserve lean mass.
5. Not recalculating as your body changes: As you lose or gain weight, your calorie needs change. A 10 kg weight loss reduces BMR by approximately 100–150 kcal/day. Failing to recalculate every 5–10 kg of weight change leads to plateaus during weight loss or unexpected gains during maintenance.
Frequently Asked Questions
What is the difference between BMR and TDEE?
BMR (Basal Metabolic Rate) is the number of calories your body burns at complete rest — just to keep your organs functioning. TDEE (Total Daily Energy Expenditure) includes BMR plus calories burned through physical activity and digestion. Your TDEE is always higher than your BMR.
How accurate is the Mifflin-St Jeor equation?
Studies show the Mifflin-St Jeor equation is accurate within about 10% for most people. It's considered more accurate than the older Harris-Benedict equation. However, individual variations in metabolism, body composition, and genetics can cause real-world differences.
Is a 500-calorie deficit safe for weight loss?
A 500 kcal/day deficit typically results in about 0.45 kg (1 lb) of weight loss per week, which is generally considered safe and sustainable. However, very active individuals or those with specific health conditions should consult a healthcare provider. Never go below 1,200 kcal/day (women) or 1,500 kcal/day (men) without medical supervision.
Why does the calculator show different calorie needs for men and women?
Men typically have higher calorie needs because they generally have more muscle mass and less body fat than women of the same height and weight. Muscle tissue is more metabolically active than fat tissue, meaning it burns more calories at rest. The Mifflin-St Jeor equation accounts for this through different constant values in the male and female formulas (+5 for males, -161 for females).
Can I use this calculator if I'm trying to build muscle?
Yes. For muscle building (hypertrophy), most nutrition experts recommend eating 200-500 calories above your TDEE (the 'Weight Gain' target shown). Pair this caloric surplus with adequate protein intake (1.6-2.2g per kg of body weight) and resistance training. A moderate surplus minimizes fat gain while providing energy for muscle growth. The calculator's macro breakdown can help you plan your protein, carb, and fat targets.
How does metabolism change with age?
Metabolic rate declines approximately 1–2% per decade after age 20, primarily due to loss of lean muscle mass (sarcopenia). A 2021 study in Science found that metabolism remains relatively stable between ages 20–60, with the sharpest decline occurring after 60. This means a 50-year-old needs roughly 150–200 fewer daily calories than they did at 25. Regular resistance training can partially offset this decline by preserving and building muscle tissue, which is more metabolically active than fat.
Should I eat back the calories I burn during exercise?
It depends on your goal. If you are maintaining weight, yes — replace exercise calories to avoid an unintentional deficit. If losing weight, eating back all exercise calories can negate your deficit. A common approach is to eat back 50–75% of estimated exercise calories, since calorie burn estimates from fitness trackers are often inflated by 20–90% according to Stanford research. The TDEE calculation already includes your general activity level, so only add back calories from extra workouts beyond your selected activity tier.
What is the thermic effect of food, and does it matter?
The thermic effect of food (TEF) is the energy required to digest, absorb, and metabolize nutrients, accounting for roughly 10% of total daily calories. Protein has the highest TEF at 20–30% of its calories, compared to 5–10% for carbohydrates and 0–3% for fat. This means a high-protein diet burns more calories through digestion alone. While TEF is already factored into general TDEE estimates, it partly explains why higher-protein diets can be advantageous for weight management beyond their satiating effect.
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