What is the Mifflin-St Jeor formula?

Developed by Mifflin et al. in 1990, it estimates basal metabolic rate: Male BMR = 10×weight(kg) + 6.25×height(cm) − 5×age + 5; Female BMR = 10×weight(kg) + 6.25×height(cm) − 5×age − 161. It is widely considered the most accurate formula for most adults.

TDEE (Total Daily Energy Expenditure) is the total number of calories you burn in a day, combining your BMR with the energy cost of your daily activities and exercise.

How accurate is this calculator?

For most adults, the Mifflin-St Jeor equation predicts resting energy expenditure within 10% of measured values. TDEE adds an activity multiplier, which adds further uncertainty. Use these figures as starting estimates and adjust based on real-world weight trends over 2–4 weeks.

Should I eat at my TDEE to maintain weight?

Yes. Eating at TDEE means consuming the same number of calories as you burn, resulting in weight maintenance over time. For fat loss, a deficit of 300–500 kcal/day is commonly recommended.

TDEE Calculator — Daily Calorie Needs

What is TDEE?

Total Daily Energy Expenditure (TDEE) is the total number of calories your body burns in a 24-hour period. It accounts for everything: the energy used to keep your heart beating and lungs breathing at rest (your Basal Metabolic Rate), the energy burned through digestion (the thermic effect of food), and the energy expended through all physical activity — from walking to the kitchen to training for a marathon.

Understanding your TDEE is the foundation of evidence-based nutrition. Whether your goal is fat loss, muscle gain, or weight maintenance, TDEE tells you the calorie target to aim for.

Basal Metabolic Rate (BMR)

BMR is the number of calories your body requires at complete rest — if you lay in bed all day and did nothing. It represents approximately 60–75% of total daily energy expenditure for most people and is driven primarily by lean body mass, age, sex, and height.

This calculator uses the Mifflin-St Jeor equation, published in 1990 in the American Journal of Clinical Nutrition. It is consistently found to be the most accurate predictive equation for BMR in healthy adults in clinical reviews, with a mean error of approximately 10% in most populations:

Male: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age(yr) + 5

Female: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age(yr) − 161

The key difference between male and female equations is the constant (+5 vs −161), reflecting average differences in body composition (males typically have greater lean muscle mass per unit of weight).

Physical Activity Level (PAL) Multipliers

To convert BMR to TDEE, we multiply by a Physical Activity Level (PAL) factor. The multipliers used in this calculator are:

Activity Level	Description	Multiplier
Sedentary	Little or no exercise; desk job	1.2
Lightly Active	Light exercise 1–3 days/week	1.375
Moderately Active	Moderate exercise 3–5 days/week	1.55
Very Active	Hard exercise 6–7 days/week	1.725
Extra Active	Very hard exercise, physical job, or twice-daily training	1.9
Athlete	Professional athlete or extreme training load	2.0

These multipliers were originally derived from doubly-labelled water (DLW) studies — the gold standard for measuring total energy expenditure in free-living humans.

Important note: The activity level is the biggest source of error in TDEE calculations. Most people overestimate their activity. When in doubt, start with the lower category and adjust based on actual weight trends over 2–3 weeks.

Macronutrient Targets

Beyond calories, this calculator estimates macronutrient targets based on your TDEE and activity level.

Protein: The recommended protein intake depends on activity:

Sedentary / Lightly Active: 0.8 g per kg of body weight — the RDA minimum, adequate for sedentary individuals
Active and Athletic: 1.6 g per kg of body weight — the level supported by a 2017 systematic review and meta-analysis by Morton et al. as optimal for maximising muscle protein synthesis

Fat: Set at 30% of total calorie intake. Adequate fat intake is essential for hormone production (including testosterone and oestrogen), absorption of fat-soluble vitamins (A, D, E, K), and cell membrane integrity.

Carbohydrates: The remainder of calories after protein and fat. Carbohydrates are the primary fuel source for high-intensity exercise. Athletes performing intense training may benefit from higher carbohydrate targets.

Using TDEE for Fat Loss and Muscle Gain

Fat loss: A moderate calorie deficit of 300–500 kcal/day below TDEE is recommended. This produces approximately 0.3–0.5 kg of fat loss per week while preserving muscle mass. Larger deficits accelerate fat loss but increase muscle loss and can impair performance, hormonal function, and recovery.

Muscle gain (bulking): A modest calorie surplus of 200–300 kcal/day above TDEE promotes muscle gain with minimal fat gain. Larger surpluses do not accelerate muscle protein synthesis but do increase fat accumulation.

Maintenance: Eating at TDEE maintains current weight. Useful for consolidation phases between fat loss and muscle-building cycles.

Why TDEE Estimates are Not Perfect

TDEE calculations are population-level predictions. Several factors cause individual variation:

Adaptive thermogenesis: When calories are restricted for extended periods, the body lowers its metabolic rate below what the equations predict — a survival mechanism. This “metabolic adaptation” (also called “starvation response”) can reduce TDEE by 5–15% after prolonged dieting.

NEAT variability: Non-Exercise Activity Thermogenesis (NEAT) — fidgeting, posture maintenance, spontaneous movement — varies dramatically between individuals (by up to 2,000 kcal/day) and decreases during calorie restriction.

Body composition: Two people with the same weight, height, age, and sex can have BMRs differing by 200–300 kcal/day due to differences in muscle-to-fat ratio.

Accuracy of food tracking: Studies show that people consistently underestimate food intake by 20–50%, often making the calorie deficit appear ineffective when the diet is simply not being followed accurately.

Practical Recommendations

Use TDEE as a starting point. Track weight daily for 2–3 weeks. If you’re not losing or gaining as expected, adjust calories by 100–200 kcal increments.
Weigh yourself consistently. Use the 7-day average weight to smooth out water retention fluctuations from salt, hormonal changes, and glycogen stores.
Recalculate as you change. Losing 5 kg changes your BMR meaningfully. Recalculate every 5–10 kg of body weight change.
Prioritise protein. High protein intake (1.6–2.0 g/kg) during fat loss protects muscle mass and increases satiety.
Adjust activity category honestly. If you have a desk job and exercise 3 times per week for 45 minutes, you are likely “Lightly Active” or at most “Moderately Active”.

Frequently Asked Questions

Why is my TDEE different from other calculators? Different calculators use different BMR equations (Mifflin-St Jeor, Harris-Benedict, Katch-McArdle) and slightly different PAL multipliers. The Mifflin-St Jeor equation used here is widely regarded as the most accurate for the general population. Differences of ±100–200 kcal are normal.

Can I use this for children or teenagers? The Mifflin-St Jeor equation is validated for adults aged 18–78. For adolescents (ages 15–17 included in this calculator), results should be treated as rough estimates. Children have higher relative energy needs for growth.

What happens if my actual weight loss doesn’t match my expected deficit? This is normal. Verify your calorie tracking accuracy using a food scale (not volume measures). Check your actual activity level. Consider that metabolic adaptation may be occurring if you have been in a deficit for more than 3–4 months.

Is eating below BMR dangerous? Eating significantly below BMR (your resting metabolic needs) for extended periods can cause muscle loss, nutrient deficiencies, hormonal disruption, and fatigue. Very low calorie diets (below 800 kcal/day) should only be undertaken under medical supervision.