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Understanding how many calories your body needs each day is the foundation of every successful weight management plan — whether you want to lose fat, build muscle, or simply maintain your current weight. This calorie calculator uses the Mifflin-St Jeor equation, the most accurate formula validated by nutrition science, to compute your Basal Metabolic Rate (BMR) and Total Daily Energy Expenditure…
## What Is BMR (Basal Metabolic Rate)? BMR is the number of calories your body burns at complete rest — just to keep you alive. It powers your heartbeat, breathing, brain function, cell repair, and body temperature regulation. BMR typically accounts for **60–75% of your total daily calorie burn**. Factors that affect BMR include: - **Body size**: Larger bodies burn more at rest - **Muscle mass**: Muscle is metabolically active — each pound burns ~6 cal/day at rest vs ~2 cal/day for fat - **Age**: BMR decreases roughly 1–2% per decade after age 20 - **Gender**: Men generally have higher BMR due to greater muscle mass - **Genetics**: Some people naturally burn faster or slower
## What Is TDEE (Total Daily Energy Expenditure)? TDEE is your total daily calorie burn — BMR plus all physical activity and the thermic effect of food (the energy your body uses to digest meals). TDEE = BMR × Activity Multiplier: | Activity Level | Multiplier | Description | |---|---|---| | Sedentary | 1.2 | Desk job, little 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 | | Extremely active | 1.9 | Physical job + intense training | Choosing the right activity level is crucial — overestimating activity is the #1 reason calorie calculators produce inaccurate results.
## How to Use Your Calorie Target **Weight loss**: Eat 500 calories below your TDEE for approximately 1 lb (0.45 kg) of fat loss per week. A 1,000-calorie deficit produces ~2 lbs/week but is aggressive and harder to sustain. Never eat below 1,200 kcal (women) or 1,500 kcal (men) without medical supervision. **Weight maintenance**: Eat at your TDEE. Track for 2 weeks — if weight is stable, the calculation is accurate. If gaining/losing, adjust by 100–200 calories. **Muscle gain**: Eat 200–500 calories above your TDEE (a "lean bulk"). Combine with progressive resistance training and high protein intake (0.7–1g per lb of body weight). **The 80/20 rule**: 80% of body composition results come from nutrition, 20% from exercise. You cannot out-train a bad diet.
Use the calorie calculator whenever you're starting a new eating plan, reviewing one that isn't working, or adjusting for a lifestyle change like a new job or training programme. It is particularly important to recalculate after losing or gaining more than 10 lbs, since calorie needs change with body weight — the target that produced a deficit at 85 kg may be close to maintenance at 78 kg.
Treating the output as a fixed prescription rather than an evidence-based starting estimate is the most damaging mistake. A 15–20% individual variation in metabolic rate means the correct calorie target can only be determined by testing the estimate against real outcomes over 2–3 weeks. A second common problem is setting an aggressive deficit on day one: very low calorie intakes increase hunger hormones, reduce energy levels, and often cause rapid initial weight loss that is mostly water, creating false expectations before the inevitable plateau.
A 40-year-old man, 6'0" (183 cm), 95 kg, moderately active has a TDEE of approximately 2,780 calories. A 500 kcal/day deficit means eating 2,280 calories — a manageable reduction that should yield roughly 0.5 kg/week. On an 800-calorie deficit (1,980/day), the short-term weight loss is faster but significantly harder to sustain, and muscle loss becomes more likely. The moderate approach reaches the same destination with far less disruption to daily life.
Mifflin-St Jeor BMR Formula
Men: BMR = (10 × kg) + (6.25 × cm) − (5 × age) + 5
Women: BMR = (10 × kg) + (6.25 × cm) − (5 × age) − 161
TDEE = BMR × Activity Multiplier
Activity multipliers: Sedentary (1.2), Light (1.375), Moderate (1.55), Active (1.725), Very Active (1.9).
A 30-year-old woman, 165 cm, 65 kg with moderate activity wants to lose weight.
Result: TDEE = 2,124 cal/day — eat ~1,624 cal/day to lose 1 lb/week
BMR is your resting metabolism — calories burned doing nothing (breathing, heartbeat, cell repair). TDEE adds physical activity and digestion energy to give your total daily calorie need.
Eat 500 calories below your TDEE for ~1 lb/week of fat loss. A 1,000-calorie deficit gives ~2 lbs/week. Never go below 1,200 kcal (women) or 1,500 kcal (men) without medical supervision.
The Mifflin-St Jeor equation (used by this calculator) is considered the most accurate for healthy adults, within ~10% of actual metabolic rate for most people.
Eat 200–500 calories above your TDEE ('lean bulk'). Combine with progressive resistance training and 0.7–1g protein per lb of body weight.
Common reasons: underestimating food intake, overestimating activity level, water retention masking fat loss, or metabolic adaptation after prolonged dieting. Track meticulously for 2 weeks and reassess.
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