What is TDEE (Total Daily Energy Expenditure)?

TDEE is the total number of calories you burn in a day, accounting for both your resting metabolism (BMR) and all physical activity. It is calculated by multiplying BMR by an activity factor (PAL) ranging from 1.2 for sedentary individuals to 1.9 for very active people. TDEE = BMR × Activity Factor.

How many calories are in 1 kg of body fat?

Pure adipose tissue contains approximately 9 kcal per gram, or 9,000 kcal per kg. However, body fat is not pure fat — it also contains water and protein. In practice, 1 kg of body fat stores approximately 7,700 kcal. This means a daily deficit of 550 kcal produces approximately 1 kg of fat loss every 14 days.

What are macronutrients and how do calories relate to them?

Macronutrients are the three major nutrients supplying dietary energy. Carbohydrates provide 4 kcal per gram; proteins provide 4 kcal per gram; fats provide 9 kcal per gram; alcohol provides 7 kcal per gram (though alcohol is not a nutrient). A 2,000 kcal balanced diet typically consists of approximately 50% carbohydrates (250 g), 20% protein (100 g), and 30% fat (67 g).

Does muscle burn more calories than fat at rest?

Yes, significantly. Skeletal muscle tissue burns approximately 13 kcal per kg per day at rest, while adipose (fat) tissue burns approximately 4.5 kcal per kg per day. This is why increasing lean muscle mass through resistance training raises your BMR over time — a process sometimes called 'metabolic investment'.

What is the activity factor (PAL) and which should I choose?

The Physical Activity Level (PAL) multiplier converts BMR to TDEE. Use: 1.2 if you have a desk job and do little or no exercise; 1.375 if you do light exercise 1–3 days per week; 1.55 if you exercise moderately 3–5 days per week; 1.725 if you do hard exercise 6–7 days per week; 1.9 if you have a very physical job or do twice-daily training. Most people overestimate their activity level — when in doubt, choose one level lower and adjust based on real-world results.

Calorie Calculator — BMR, TDEE & Daily Calorie Needs (2025 Guide)

Nutrition Science Weight Management Health & Fitness BMR Calculator TDEE Calculator

Whether you're aiming to lose body fat, build muscle, or simply maintain a healthy weight, understanding how many calories your body actually needs each day is the single most powerful starting point. The free HeLovesMath Calorie Calculator uses the gold-standard Mifflin-St Jeor equation — endorsed by the Academy of Nutrition and Dietetics — to calculate your Basal Metabolic Rate (BMR) and Total Daily Energy Expenditure (TDEE), then delivers three personalised daily calorie targets: for maintenance, fat loss, and lean muscle gain.

Below the calculator you will find a comprehensive, science-backed guide covering: the mathematics of BMR and TDEE with fully rendered formulas, a comparison of all major calorie estimation methods, an explanation of macronutrient calorie values, activity multipliers, four worked calculation examples, and a 12-question FAQ. This is not a generic rewrite — it is a deeply researched reference you can bookmark and return to.

Free Online Calorie Calculator (BMR & TDEE)

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Valid range: 15 – 80

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Valid range: 15 – 80

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✅ Your Personalised Calorie Results

Basal Metabolic Rate (BMR): — kcal/day

Total Daily Energy Expenditure (TDEE): — kcal/day

⚖️ Maintain Weight

—

kcal / day

🔥 Lose Weight

—

kcal / day (−500 deficit)

💪 Gain Muscle

—

kcal / day (+500 surplus)

Calories (kcal)

⇄

Kilojoules (kJ)

What Is a Calorie? The Physics of Food Energy

The word calorie is used in two distinct ways that cause tremendous confusion. The small calorie (cal) is a unit of heat energy defined as the amount of energy required to raise the temperature of 1 gram of water by 1 °C at 1 atm pressure. The kilocalorie (kcal), equal to 1,000 small calories, is what nutritionists mean when they say "calorie" on a food label. In the United States, the Calorie (capital C) on nutrition labels is always the kilocalorie.

✦ Definition — The Thermochemical Calorie

\[1\ \text{kcal} = 4.1868\ \text{kJ} \qquad \Longleftrightarrow \qquad 1\ \text{kJ} = \frac{1}{4.1868}\ \text{kcal} \approx 0.2390\ \text{kcal}\]

This exact factor (4.1868) is the International Table calorie, adopted by the 5th International Conference on the Properties of Steam (1956) and used on EU, Australian, and UK food labels.

In a biological context, calories represent the chemical energy stored in the bonds of food molecules (carbohydrates, fats, proteins, and alcohol). When these molecules are metabolised — primarily through oxidation reactions — the stored energy is released and used to drive three things: mechanical work (muscle contraction), biosynthesis (building new cells and molecules), and heat production (thermoregulation).

✦ Energy Balance Equation (First Law of Thermodynamics applied to the body)

\[\Delta E_{\text{body}} = E_{\text{in}} - E_{\text{out}}\]

E_in = dietary energy intake (kcal/day) | E_out = total energy expenditure — BMR + TEF + NEAT + EAT (kcal/day) | When E_in > E_out: weight gain. When E_in < E_out: weight loss. When E_in = E_out: weight maintenance.

BMR — Basal Metabolic Rate: Formulas & Science

Your Basal Metabolic Rate (BMR) is the minimum number of kilocalories your body requires over 24 hours to sustain its essential physiological functions while at complete rest in a thermoneutral (comfortable-temperature) environment, in a post-absorptive (fasted) state. It accounts for the energy cost of breathing, maintaining heartbeat, ionic gradients across cell membranes, protein synthesis, hormone secretion, and brain activity.

BMR typically represents 60–75% of total daily energy expenditure for sedentary individuals. It is primarily determined by lean body mass, since muscle tissue is metabolically far more active than fat tissue at rest (~13 kcal/kg/day vs. ~4.5 kcal/kg/day for fat).

The Mifflin-St Jeor Equation (Recommended)

Developed by Mifflin, St Jeor, Hill, and Scott in 1990 and validated in numerous subsequent studies, the Mifflin-St Jeor equation is the most accurate general-population formula for estimating BMR from easily measured variables: weight, height, age, and sex.

✦ Mifflin-St Jeor BMR — Men

\[\text{BMR}_{\text{male}} = 10W + 6.25H - 5A + 5\]

W = body weight in kilograms (kg) | H = height in centimetres (cm) | A = age in years | Result in kcal/day

✦ Mifflin-St Jeor BMR — Women

\[\text{BMR}_{\text{female}} = 10W + 6.25H - 5A - 161\]

The only difference from the male formula is the constant: +5 for males vs. −161 for females. This 166 kcal/day gap reflects the typical difference in body composition (males have proportionally more metabolically active muscle mass).

The Original Harris-Benedict Equation (1919)

The Harris-Benedict equation was the gold standard for most of the 20th century. It was revised by Roza and Shizgal in 1984 to correct for a systematic overestimation in the original formula.

✦ Revised Harris-Benedict — Men (Roza & Shizgal, 1984)

\[\text{BMR}_{\text{male}} = 88.362 + 13.397W + 4.799H - 5.677A\]

✦ Revised Harris-Benedict — Women (Roza & Shizgal, 1984)

\[\text{BMR}_{\text{female}} = 447.593 + 9.247W + 3.098H - 4.330A\]

The Katch-McArdle Equation (Uses Lean Body Mass)

If you have had a DEXA scan or body composition test and know your lean body mass (LBM), the Katch-McArdle formula is the most accurate of all — because BMR is almost entirely determined by metabolically active tissue, not fat mass.

✦ Katch-McArdle BMR (requires lean body mass)

\[\text{BMR} = 370 + 21.6 \times \text{LBM}\]

LBM = lean body mass in kilograms = total weight × (1 − body fat fraction). Example: 80 kg at 20% body fat → LBM = 80 × 0.80 = 64 kg → BMR = 370 + 21.6 × 64 = 1,752.4 kcal/day.

TDEE — Total Daily Energy Expenditure & Activity Multipliers

Your BMR only tells you what you'd burn lying completely still for 24 hours. In real life, you move, digest food, and maintain body temperature — all of which burn additional calories. The Total Daily Energy Expenditure (TDEE) is calculated by multiplying BMR by a Physical Activity Level (PAL) factor:

✦ TDEE Calculation

\[\text{TDEE} = \text{BMR} \times \text{PAL}\]

PAL = Physical Activity Level multiplier (dimensionless, range 1.2 – 1.9)

Activity Factor (PAL) Reference Table

Activity Level	PAL Factor	Description	Typical Person
Sedentary	× 1.200	Little or no exercise	Office worker, minimal walking
Lightly Active	× 1.375	Exercise 1–3 days/week	Occasional gym-goer, light walking
Moderately Active	× 1.550	Exercise 3–5 days/week	Regular gym, 30–60 min/day
Very Active	× 1.725	Hard exercise 6–7 days/week	Dedicated athlete, daily training
Extra Active	× 1.900	Physical job + daily training	Construction worker + gym; elite athlete

⚠️ Important: Research consistently shows that most people overestimate their activity level by at least one category. If you sit at a desk most of the day and exercise 3–4 times per week for 45 minutes, choose Lightly Active or Moderately Active — not Very Active. When uncertain, choose the lower option and adjust based on 2–3 weeks of real-world results.

Macronutrients & Their Calorie Values

All dietary energy comes from four sources — the three macronutrients and alcohol. Understanding their calorie densities is essential for creating a real-world meal plan from your TDEE target.

✦ Atwater General Factors — Caloric Density of Macronutrients

\[E_{\text{carb}} = 4\ \text{kcal/g} \qquad E_{\text{protein}} = 4\ \text{kcal/g} \qquad E_{\text{fat}} = 9\ \text{kcal/g} \qquad E_{\text{alcohol}} = 7\ \text{kcal/g}\]

These are the Atwater general factors, established by Wilbur Atwater in the 1890s and still used on virtually all nutrition labels worldwide. Dietary fibre contributes approximately 2 kcal/g in practice (partly fermented by gut bacteria).

How to Calculate Macronutrient Grams from a Calorie Target

✦ Grams per Macronutrient from Calorie Target

\[g_{\text{macro}} = \frac{\%_{\text{macro}} \times \text{TDEE}}{E_{\text{macro}}}\]

Example: On a 2,200 kcal TDEE with a 50/20/30 carb/protein/fat split:
Carbs: (0.50 × 2200) / 4 = 275 g | Protein: (0.20 × 2200) / 4 = 110 g | Fat: (0.30 × 2200) / 9 = 73 g

🍞 Carbohydrates — 4 kcal/g

The body's preferred fuel source for the brain and high-intensity exercise. Stored as glycogen in liver and muscles (≈ 400–600 g total). Excess is converted to fat via de novo lipogenesis. Recommended: 45–65% of total calories (Dietary Guidelines 2020-2025).

🥩 Protein — 4 kcal/g

Essential for muscle maintenance, immune function, enzymes, and hormones. Has the highest thermic effect of food (20–35%). Recommended intake for active adults: 1.6–2.2 g/kg of body weight/day for muscle preservation during a calorie deficit (International Society of Sports Nutrition, 2017).

🥑 Dietary Fat — 9 kcal/g

Highest energy density of all macronutrients. Essential for fat-soluble vitamins (A, D, E, K), hormone synthesis, and cell membrane integrity. Despite its calorie density, dietary fat does not directly cause body fat gain — total calorie balance does. Recommended: 20–35% of total calories.

🍺 Alcohol — 7 kcal/g

Often called the "fourth macronutrient," alcohol provides nearly twice the calories of carbs and protein per gram. The body prioritises alcohol oxidation over all other fuels, effectively pausing fat burning while alcohol is present. Alcohol provides energy but zero nutritional value.

Calorie Targets for Weight Loss, Maintenance & Muscle Gain

The 3,500 kcal Rule and Its Modern Refinement

The widely cited rule that "3,500 kcal = 1 lb of fat loss" dates to Max Wishnofsky's 1958 paper. It remains a useful rough guide but oversimplifies a dynamic system. The dynamic energy balance model (Hall et al., 2012) shows that as body weight changes, BMR changes too — so a fixed deficit produces diminishing returns over time as the body adapts.

✦ Approximate Weight Change from Calorie Deficit/Surplus

\[\Delta W_{\text{fat}} \approx \frac{\Delta E_{\text{daily}} \times \text{days}}{7{,}700\ \text{kcal/kg}}\]

ΔE_daily = daily calorie deficit (−) or surplus (+) in kcal/day | 7,700 kcal/kg = approximate energy content of 1 kg of body fat tissue | Example: −500 kcal/day × 14 days ÷ 7,700 = −0.91 kg in 2 weeks (approximately).

⚖️ Maintain Weight

Eat at your full TDEE. This is the calorie blueprint for body recomposition (building muscle while maintaining weight) when combined with progressive resistance training and adequate protein (≥1.6 g/kg).

🔥 Lose Fat — TDEE − 500 kcal

Creates approximately 0.45 kg (1 lb) of fat loss per week. This is the maximum recommended deficit for most people without significant risk of muscle loss (provided protein intake is ≥1.6–2.2 g/kg). A moderate deficit preserves metabolic rate better than aggressive restriction.

💪 Gain Muscle — TDEE + 500 kcal

A modest surplus of 250–500 kcal/day supports muscle hypertrophy (growth) with minimal fat gain in natural athletes performing progressive resistance training. "Dirty bulking" (1,000+ kcal surplus) primarily adds body fat, not muscle.

Minimum Safe Intakes: The National Institutes of Health and most registered dietitians recommend never going below 1,200 kcal/day for women or 1,500 kcal/day for men without medical supervision. Very-low-calorie diets (VLCDs, <800 kcal/day) are only appropriate under a physician's direct care due to risks of gallstones, electrolyte imbalances, and nutrient deficiencies.

Beyond BMR: TEF, NEAT & EAT — The Complete Energy Expenditure Picture

TDEE = BMR × PAL is a useful simplification, but the full picture of daily energy expenditure has four distinct components:

✦ Full TDEE Decomposition

\[\text{TDEE} = \underbrace{\text{BMR}}_{\approx 60\text{–}75\%} + \underbrace{\text{TEF}}_{\approx 10\%} + \underbrace{\text{NEAT}}_{\approx 15\text{–}30\%} + \underbrace{\text{EAT}}_{\text{variable}}\]

BMR = Basal Metabolic Rate (resting energy expenditure) | TEF = Thermic Effect of Food (energy cost of digesting and absorbing food) | NEAT = Non-Exercise Activity Thermogenesis (all movement that is not formal exercise — fidgeting, posture, walking around the house) | EAT = Exercise Activity Thermogenesis (planned workouts)

🌡️ TEF — Thermic Effect of Food (~10%)

The energy cost of digesting, absorbing, and metabolising food. Protein: 20–35%. Carbohydrates: 5–10%. Fat: 0–3%. A high-protein diet increases TEF noticeably — another reason protein is recommended during weight loss.

🚶 NEAT — Non-Exercise Activity (variable)

The most variable component of TDEE — it can range from 100 kcal/day in very sedentary individuals to >2,000 kcal/day in physically active occupations. Research (Levine et al., 2000) shows natural "fidgeters" burn up to 350 kcal/day more than non-fidgeters. NEAT is highly responsive to changes in calorie intake.

🏋️ EAT — Exercise Activity (variable)

Planned structured exercise. Walking at 5 km/h burns ~280 kcal/hour (70 kg person). Running at 10 km/h burns ~600 kcal/hour. Resistance training burns 200–400 kcal/hour. Note: EAT is often a smaller fraction of TDEE than most people expect — diet is far more powerful than exercise for creating a calorie deficit.

BMR Formula Comparison — Accuracy & Use Case

Formula	Year	Inputs Required	Accuracy vs. Indirect Calorimetry	Best For
Mifflin-St Jeor	1990	W, H, A, Sex	±10% for ~82% of people	General population — recommended by AND
Harris-Benedict (revised)	1984	W, H, A, Sex	±10% for ~68% of people	Historical comparison, clinical nutrition
Katch-McArdle	1996	Lean body mass only	Most accurate if LBM is known	Athletes, post-DEXA scan
Schofield	1985	W, Sex, Age group	Similar to H-B revised	WHO/FAO nutrition applications
Owen	1988	W, Sex	Lower accuracy (ignores H & A)	Quick approximation only

Bottom line: The Mifflin-St Jeor equation is the most accurate formula for estimating BMR without laboratory equipment. This is why HeLovesMath's calorie calculator uses it as the default. If you have had body composition testing, the Katch-McArdle formula will give you a more personalised result.

Worked Examples — Step-by-Step BMR & TDEE Calculations

Example 1 — Male, 28 years, 80 kg, 180 cm, Moderately Active

Apply Mifflin-St Jeor (male): \(\text{BMR} = 10W + 6.25H - 5A + 5\)

\(\text{BMR} = 10(80) + 6.25(180) - 5(28) + 5 = 800 + 1125 - 140 + 5 = 1790\ \text{kcal/day}\)

Moderately Active → PAL = 1.55. Therefore: \(\text{TDEE} = 1790 \times 1.55 = 2774\ \text{kcal/day}\)

Goals: Maintain = 2,774 kcal | Lose = 2,274 kcal | Gain = 3,274 kcal

✅ Result: BMR = 1,790 kcal/day | TDEE = 2,774 kcal/day

Example 2 — Female, 35 years, 65 kg, 165 cm, Lightly Active

Apply Mifflin-St Jeor (female): \(\text{BMR} = 10W + 6.25H - 5A - 161\)

\(\text{BMR} = 10(65) + 6.25(165) - 5(35) - 161 = 650 + 1031.25 - 175 - 161 = 1345.25\ \text{kcal/day}\)

Lightly Active → PAL = 1.375. Therefore: \(\text{TDEE} = 1345.25 \times 1.375 \approx 1850\ \text{kcal/day}\)

Goals: Maintain = 1,850 kcal | Lose = 1,350 kcal | Gain = 2,350 kcal

✅ Result: BMR = 1,345 kcal/day | TDEE = 1,850 kcal/day

Example 3 — Converting Weight from Pounds/Feet to kg/cm (US to Metric)

Height: 5 ft 10 in = (5 × 12 + 10) = 70 total inches. Convert: \(70 \times 2.54 = 177.8\ \text{cm}\)

Weight: 175 lbs. Convert: \(175 \div 2.2046 = 79.4\ \text{kg}\)

Male, 40 years: \(\text{BMR} = 10(79.4) + 6.25(177.8) - 5(40) + 5 = 794 + 1111.25 - 200 + 5 = 1710.25\ \text{kcal/day}\)

Very Active (PAL 1.725): \(\text{TDEE} = 1710.25 \times 1.725 \approx 2950\ \text{kcal/day}\)

✅ Result: BMR ≈ 1,710 kcal/day | TDEE ≈ 2,950 kcal/day

Example 4 — Converting 2,000 kcal to Kilojoules

Conversion factor: 1 kcal = 4.1868 kJ (International Table)

\(2000\ \text{kcal} \times 4.1868 = 8{,}373.6\ \text{kJ} \approx 8.37\ \text{MJ}\)

This is why Australian food labels typically show values around 8,500 kJ for a 2,000 kcal diet — the same quantity of energy expressed differently.

✅ Answer: 2,000 kcal = 8,373.6 kJ

Frequently Asked Questions (12 Q&As)

What is BMR (Basal Metabolic Rate)?＋

BMR is the number of calories your body burns at complete rest to sustain vital functions — breathing, circulation, cell production, and temperature regulation. It represents roughly 60–75% of total daily calorie expenditure. For a 30-year-old male weighing 80 kg at 180 cm, BMR ≈ 1,790 kcal/day using the Mifflin-St Jeor equation: \(\text{BMR} = 10(80) + 6.25(180) - 5(30) + 5 = 1890\ \text{kcal/day}.\)

What is TDEE and how is it calculated?＋

TDEE (Total Daily Energy Expenditure) is the total number of calories you burn in a day, including all activity. It equals BMR multiplied by your Physical Activity Level (PAL): \(\text{TDEE} = \text{BMR} \times \text{PAL}\). PAL ranges from 1.2 (sedentary) to 1.9 (extremely active). TDEE is your maintenance calorie level.

Which BMR formula is the most accurate — Mifflin-St Jeor or Harris-Benedict?＋

The Mifflin-St Jeor equation (1990) is consistently more accurate than the original Harris-Benedict equation (1919). A landmark 2005 study in the Journal of the American Dietetic Association found Mifflin-St Jeor predicted measured resting energy expenditure within 10% for 82% of subjects, compared to 68% for the revised Harris-Benedict. The Academy of Nutrition and Dietetics recommends Mifflin-St Jeor as the preferred method.

How many calories should I eat to lose weight safely?＋

A deficit of 500 kcal/day below your TDEE produces approximately 0.45 kg (1 lb) of fat loss per week — a safe, sustainable rate. This follows from: 1 kg of body fat ≈ 7,700 kcal, so a 500 kcal/day deficit = 3,500 kcal/week ÷ 7,700 ≈ 0.45 kg/week. Never go below 1,200 kcal/day (women) or 1,500 kcal/day (men) without medical supervision.

How many kcal are in 1 kg of body fat?＋

Approximately 7,700 kcal per kg of body fat tissue (or ~3,500 kcal per pound). Pure fat contains 9 kcal/g = 9,000 kcal/kg, but body fat also contains water and protein, bringing the practical figure to ~7,700 kcal/kg. Using the formula: \(\Delta W \approx \Delta E_{\text{daily}} \times \text{days} \div 7700\) gives a rough weekly fat loss projection.

What does 1 kcal equal in kilojoules?＋

\(1\ \text{kcal} = 4.1868\ \text{kJ}\). Conversely, \(1\ \text{kJ} \approx 0.239\ \text{kcal}\). Food labels in Australia, the UK, and the EU often show both values. A common 2,000 kcal reference diet equals \(2000 \times 4.1868 = 8{,}373.6\ \text{kJ} \approx 8.4\ \text{MJ}\) per day.

What are macronutrients and how many calories does each provide?＋

Macronutrients are the three main classes of energy-providing nutrients: carbohydrates (4 kcal/g), proteins (4 kcal/g), and fats (9 kcal/g). Alcohol provides 7 kcal/g but is not a nutrient. To find grams of each macro: \(g = (\%\text{ of calories} \times \text{TDEE}) \div \text{kcal per gram}\). For example, 25% protein on 2,000 kcal = 500 ÷ 4 = 125 g protein/day.

Does muscle burn more calories than fat?＋

Yes. Skeletal muscle metabolises approximately 13 kcal per kg per day at rest, while adipose (fat) tissue metabolises approximately 4.5 kcal per kg per day at rest. A person with 10 kg more lean muscle mass will burn roughly 85 more kcal/day just at rest — not dramatic on a daily basis, but compounding meaningfully over months and years.

What is the thermic effect of food (TEF)?＋

TEF is the energy your body uses to digest, absorb, transport, and store food. It accounts for roughly 10% of TDEE. Protein has the highest TEF (20–35% of its calories are burned during metabolism), followed by carbohydrates (5–10%) and fat (0–3%). Eating a high-protein diet slightly increases your daily calorie burn through this mechanism.

How does age affect calorie needs?＋

BMR declines approximately 1–2% per decade from age 20, primarily due to muscle loss (sarcopenia) and changes in organ metabolic rates. The Mifflin-St Jeor equation captures this with the \(-5A\) term — each additional year of age reduces BMR by 5 kcal/day. A 50-year-old has a BMR approximately 150 kcal lower than a 20-year-old of the same weight and height. This is why calorie needs decrease with age and why resistance training (which preserves muscle) is particularly important as you age.

What is NEAT and why does it matter for weight management?＋

NEAT (Non-Exercise Activity Thermogenesis) is all the energy burned through movement that is not planned exercise — walking to the kitchen, fidgeting, gesturing while talking, maintaining posture. Research by James Levine at the Mayo Clinic found NEAT can vary by up to 2,000 kcal/day between individuals of similar size. When people restrict calories, NEAT often unconsciously decreases (you sit more, fidget less) — this "adaptive thermogenesis" is a primary reason weight loss slows over time.

Is calorie counting the only way to lose weight?＋

No — calorie balance is the mechanism, but you do not need to count every calorie to achieve it. Effective strategies that naturally create a calorie deficit without tracking include: eating more high-fibre whole foods (which increase satiety at lower calorie loads), reducing ultra-processed foods (which are engineered to override satiety signals), intermittent fasting patterns, portion control, and increasing daily step count (NEAT). Understanding your TDEE is still extremely valuable as a reference point, even if you don't actively count calories.