BMR / TDEE Calculator
Estimate your daily calorie needs using the revised Harris-Benedict equation, then adjust for activity to get your Total Daily Energy Expenditure (TDEE) — the rough number of calories you burn in 24 hours when you eat a maintenance diet. Enter your weight in kilograms, height in centimetres, age, biological sex, and an activity multiplier (sedentary 1.2, lightly active 1.375, moderately active 1.55, very active 1.725, extremely active 1.9). The result is what most nutrition guides call your "maintenance calories" — a starting point for designing a deficit (to lose weight), a surplus (to gain muscle), or a recomposition plan.
About this calculator
The calculator uses the revised Harris-Benedict equation (Roza & Shizgal, 1984), which gives basal metabolic rate (BMR) in kcal/day: • Male: BMR = 88.362 + (13.397 × weight kg) + (4.799 × height cm) − (5.677 × age) • Female: BMR = 447.593 + (9.247 × weight kg) + (3.098 × height cm) − (4.330 × age) BMR is the energy your body burns at complete rest — keeping your heart beating, lungs breathing, brain firing, organs running, and body temperature regulated. It accounts for roughly 60–75% of total daily energy expenditure for most people. The calculator then multiplies BMR by an activity factor to estimate TDEE: 1.2 for sedentary (desk job, little or no exercise), 1.375 for lightly active (light exercise 1–3 days/week), 1.55 for moderately active (moderate exercise 3–5 days/week), 1.725 for very active (hard exercise 6–7 days/week), and 1.9 for extremely active (very hard exercise or a physical job). Why Harris-Benedict and not Mifflin-St Jeor? The Mifflin equation (1990) is slightly more accurate for the modern population on average — its 95% confidence interval is narrower — but the revised Harris-Benedict remains standard in many clinical and fitness contexts and produces estimates within ~5% of Mifflin for typical body sizes. Edge cases: BMR formulas were derived from average healthy adults and are less accurate at the extremes — very lean, very muscular, very obese, very tall, very short, very old, very young. They also do not account for medical conditions affecting metabolism (hyperthyroidism, hypothyroidism, fever, recent surgery). Real measured BMR via indirect calorimetry can differ from the predicted value by 10–15% even in healthy adults, so treat the calculator output as a starting point you refine by tracking weight changes against actual intake over 2–3 weeks.
How to use
Example 1 — Moderately active man. A 30-year-old male weighing 80 kg and standing 180 cm, exercising 4 times a week. Enter 80, 180, 30, male, and 1.55 (moderately active). BMR = 88.362 + (13.397 × 80) + (4.799 × 180) − (5.677 × 30) = 88.362 + 1071.76 + 863.82 − 170.31 ≈ 1853.6 kcal/day. TDEE = 1853.6 × 1.55 ≈ 2873 kcal/day. ✓ To lose about 0.5 kg per week, aim to eat roughly 2300 kcal/day (a 500-kcal daily deficit, which equals approximately 3500 kcal per week — the rough caloric equivalent of half a kilogram of body fat). Example 2 — Lightly active woman. A 45-year-old female weighing 65 kg and standing 165 cm, walking most days but no structured exercise. Enter 65, 165, 45, female, and 1.375 (lightly active). BMR = 447.593 + (9.247 × 65) + (3.098 × 165) − (4.330 × 45) = 447.593 + 601.06 + 511.17 − 194.85 ≈ 1365 kcal/day. TDEE = 1365 × 1.375 ≈ 1877 kcal/day. ✓ Maintenance is around 1877 calories; weight gain at a rate of about 0.25 kg per week would require eating approximately 2150 kcal/day.
Frequently asked questions
What is the difference between BMR and TDEE?
BMR (Basal Metabolic Rate) is the energy your body burns at complete rest in a thermally neutral environment after a 12-hour fast — essentially the baseline cost of staying alive. TDEE (Total Daily Energy Expenditure) is BMR plus everything else: the thermic effect of food (~10% of TDEE), non-exercise activity thermogenesis (fidgeting, standing, walking around, ~15% in a sedentary person and much more in an active one), and intentional exercise. The calculator labels its output as "Daily Calorie Needs" because it actually returns TDEE (BMR × activity multiplier), not pure BMR — for the unmodified BMR figure, set the activity level to 1.0. TDEE is the operational number for almost all weight-management goals; pure BMR is mainly useful as a research or clinical baseline.
Which BMR equation is the most accurate?
The Mifflin-St Jeor equation (1990) is now considered the gold standard for predicting BMR in non-obese healthy adults — multiple validation studies have shown it has the narrowest error band of the major prediction equations. The revised Harris-Benedict (used by this calculator) is a close second and tends to estimate BMR a few percent higher than Mifflin for the same person. The Katch-McArdle equation is more accurate than either for very lean or very muscular people because it incorporates lean body mass directly, but it requires a body-fat measurement most people do not have. Schofield equations remain widely used in clinical pediatric and geriatric settings. For almost all practical purposes, any of these will get you within 5–10% of your true BMR — and the bigger source of error is usually the activity multiplier, which is essentially a guess.
How accurate are the activity multipliers?
The activity multipliers (1.2, 1.375, 1.55, 1.725, 1.9) are population-average rules of thumb and frequently overstate real expenditure, especially for people who self-classify as "moderately active" or higher. Studies using doubly-labelled water (the gold-standard method for measuring real energy expenditure) consistently show that self-reported activity levels overestimate true expenditure by 10–30%, partly because people overestimate how much they exercise and partly because NEAT (non-exercise movement) drops in compensation when structured exercise increases. A reliable approach is to start with the calculated TDEE, eat at that level for 2–3 weeks while tracking weight, then adjust by ±100–200 calories per day depending on whether weight is stable, rising, or falling. The number the calculator gives you is a starting hypothesis to test, not a fixed truth.
What are the most common mistakes people make using calorie calculators?
The most common is choosing too high an activity multiplier — most people who say they are "very active" are really lightly to moderately active when measured objectively, so they overeat thinking they are at maintenance. The second is treating the output as exact: real metabolic rates vary 10–15% between individuals of identical age, sex, height, and weight, so the calculator is a starting estimate, not a diagnosis. The third is forgetting that BMR drops as you lose weight (you burn less because there is less of you to feed), so the maintenance number you calculated 10 kg ago is no longer valid. The fourth is ignoring tracking error in calorie intake: under-reporting of food intake is so universal in nutrition studies that it has its own name (the "memory deficit"), and the effect is typically 20–40% in self-reported diet logs. Finally, people swing wildly between large deficits and surpluses; sustained, modest deficits of 300–500 kcal/day are far more sustainable than 1000+ kcal/day crash dieting.
When should I not use this calculator?
Do not use it if you are under 18 — children and adolescents have different metabolic rates and require pediatric equations (Schofield is standard). Skip it during pregnancy and lactation, which add roughly 300 and 500 kcal/day to maintenance respectively, and require dedicated calculators. It is unreliable for people with significant medical conditions affecting metabolism (untreated thyroid disorders, recent major surgery, severe burns, cancer cachexia, eating-disorder recovery) — those situations require clinical assessment and often indirect calorimetry to measure BMR directly. It is also a poor fit at the extremes of body composition: very lean bodybuilders (high lean mass relative to weight) and very obese individuals both fall outside the populations the equations were derived from. For all of these situations, talk to a registered dietitian or sports medicine physician rather than relying on a single online estimate.