Science-Based · Free · Instant
Three peer-reviewed equations. One clear recommendation. No signup, no ads on results — just your numbers.
Calculate My Calories ↓Browse thousands of foods with calories, macros, and micronutrients — 450+ dishes across 12 world cuisines plus a global whole-food database.
All calculations run instantly in your browser. No data is sent to any server.
Basal Metabolic Rate (BMR) is the minimum calories your body needs to sustain life at complete rest — breathing, circulation, cell production, and temperature regulation.
BMR typically accounts for 60–75% of total daily calorie expenditure. Higher muscle mass increases BMR, which is why resistance training supports long-term fat loss.
Total Daily Energy Expenditure (TDEE) is your complete daily calorie burn — BMR multiplied by an activity factor that accounts for exercise, NEAT, and the thermic effect of food.
Eating at your TDEE = maintenance. Below = fat loss. Above = weight gain. This energy balance principle is the foundation of evidence-based nutrition.
Mifflin-St Jeor (1990) — derived from 498 subjects, validated as the most accurate general-population formula. Predicts BMR within 10% for 82% of individuals.
Harris-Benedict (Revised 1984) — revised by Roza & Shizgal. Runs ~5% higher, more appropriate for very active individuals.
Cunningham (1980) — uses lean body mass, bypassing sex correction. Most accurate with a reliable body fat % measurement.
One pound of fat stores approximately 3,500 kcal. A daily deficit of 500 kcal produces ≈ 0.5 kg (1 lb) of fat loss per week — the NIH-recommended guideline.
Deficits greater than 750 kcal/day risk muscle loss, hormonal disruption, and nutrient deficiencies. High protein intake (≥1.6 g/kg) and resistance training help preserve lean mass during any deficit.
| Level | Multiplier | Description |
|---|---|---|
| Sedentary | ×1.2 | Desk job, no exercise |
| Lightly Active | ×1.375 | Exercise 1–3 days/week |
| Moderately Active | ×1.55 | Exercise 3–5 days/week |
| Very Active | ×1.725 | Hard exercise 6–7 days/week |
| Extra Active | ×1.9 | Physical job or 2× daily training |
The Mifflin-St Jeor equation predicts measured BMR within ±10% in about 82% of people when validated against indirect calorimetry. The main source of error is the activity multiplier — most people overestimate their activity level. Using a fitness tracker can improve accuracy significantly.
Eating below your BMR for extended periods is not recommended. Your BMR represents the minimum energy your body needs for vital organ function. Very low calorie diets carry risks of muscle loss, micronutrient deficiencies, metabolic adaptation, and gallstones. Always consult a dietitian for supervised very-low-calorie approaches.
Most people underestimate their calorie needs. The activity multipliers account for all movement — gym sessions, NEAT (fidgeting, walking), and the thermic effect of food (≈10% of calories burned during digestion). If results seem high, track at your calculated TDEE for 2–3 weeks and compare actual weight change before adjusting.
From most to least accurate: DEXA scan (±1–2%), hydrostatic weighing (±2%), Bod Pod (±2–3%), 3–7 site skinfold calipers (±3%), bioelectrical impedance scales (±3–5%, inconsistent), Navy tape measure method (±3–5%). For the Cunningham equation, DEXA or multi-site calipers are recommended.
BMR is measured under strict conditions — complete rest, fasted state, thermoneutral environment. RMR is measured at rest without the strict conditions. RMR is typically 10–20% higher than BMR. Most practical calculators measure RMR but label it BMR — the distinction rarely matters for daily planning.
A 500 kcal/day deficit yields ≈0.5 kg fat loss per week. The scale may show larger initial drops (water weight from glycogen depletion) then stabilize. Visible changes typically appear after 4–8 weeks for most people, depending on starting body composition.
For most people, a consistent daily target works well. Calorie cycling can improve training performance and dietary adherence for some, but research shows similar fat loss outcomes when weekly totals are equal. Choose whichever approach you can maintain consistently.
The evidence-based recommendation for muscle preservation during a deficit is 1.6–2.2 g/kg body weight (0.73–1.0 g/lb). Higher intakes (up to 3.1 g/kg) are used in aggressive deficits for lean, resistance-trained individuals. Protein has the highest satiety per calorie and the highest thermic effect (20–35%).
Yes — this is adaptive thermogenesis. TDEE decreases 5–15% below predicted during a sustained deficit through reduced NEAT, lower hormone levels (leptin, T3), and reduced body weight. Recalculate your TDEE every 4–8 weeks during a cut, and consider diet breaks at maintenance every 8–12 weeks.
FDA regulations allow up to ±20% error on nutrition labels. Research shows restaurant calorie counts can be off by 100–300 kcal per meal. For reliable tracking, weigh food with a kitchen scale rather than using volume measurements, and be aware that food databases have inherent inaccuracies. Trend tracking over weeks beats day-to-day precision.
NEAT (Non-Exercise Activity Thermogenesis) is all movement that isn't formal exercise: fidgeting, standing, walking, typing. Mayo Clinic research shows NEAT can range from 200 kcal/day in sedentary individuals to over 1,000 kcal/day in highly active people. Increasing daily steps is one of the most practical ways to increase TDEE.
Protein has a higher thermic effect (20–35% burned during digestion) vs carbs (5–10%) and fat (0–3%). However, the energy balance principle holds across all macronutrients — no macronutrient is uniquely fattening or fat-burning when calories are controlled. Macros matter for performance, satiety, and health markers.
A lean bulk surplus of 200–300 kcal/day above TDEE, with ≥1.6 g/kg protein and consistent progressive resistance training, maximizes muscle gain while minimizing fat gain. Research suggests natural muscle gain rates of approximately 0.5–1 kg/month for trained individuals — so very large surpluses primarily add fat.
BMR decreases approximately 1–2% per decade after age 20, largely due to sarcopenia (muscle loss). The decline accelerates after age 60. Maintaining muscle mass through resistance training partially offsets this decline. Calorie needs also decrease as body weight decreases with age.
Each equation was derived from a different population using different regression methods. Mifflin-St Jeor used 498 subjects in 1990. Harris-Benedict used 239 subjects (1919, revised 1984). Cunningham used lean body mass. Differences of 50–200 kcal between methods are normal and expected.
Drinking cold water causes a small thermogenic effect as the body heats it to core temperature. A 500 mL glass may temporarily increase metabolic rate by ≈3% for 30–40 minutes, burning approximately 8 kcal. Real, but too small to be meaningful for weight loss. Adequate hydration does support optimal metabolic function.
1) Use a food scale to weigh in grams (not cups/spoons). 2) Log everything, including oils, sauces, and drinks. 3) Use verified entries in apps (Cronometer, MyFitnessPal) not user-submitted ones. 4) Track 2–4 weeks and compare against actual weight change to calibrate your true TDEE.
Women generally have lower BMR than men of the same size due to differences in average body composition — specifically lower average muscle mass (metabolically active) and higher average fat mass (not). The equations account for this with sex-specific constants. There's no inherent reason women need less — the difference comes from body composition.
A plateau after 3+ consistent weeks means your TDEE has dropped to match intake. Options: 1) Recalculate TDEE at your new lower body weight. 2) Increase daily steps (NEAT). 3) Add or intensify structured exercise. 4) Diet break at TDEE for 1–2 weeks to restore leptin. 5) Recheck food tracking accuracy.
Short-term rates of 1–1.5 kg/week can be medically appropriate for individuals with BMI >35 under professional supervision. For lean individuals, faster rates risk muscle loss, bone density reduction, and hormonal disruption. The 0.5–1 kg/week guideline is a safe range for unsupervised general population use.
