Skip to content

Free Nutrition Tool

Calorie Calculator

Estimate your daily calorie target for fat loss, maintenance, or muscle gain using the Mifflin-St Jeor equation, considered the most accurate BMR formula for the general population.

Mifflin-St Jeor equation Macro breakdown included Free, no sign-up

Enter Your Details

All fields affect your result. Be honest with activity level for the most accurate estimate.

Between 15 and 100

Gender

Height in centimetres

Enter your current body weight in kg.

How to Use This Calculator

  1. Enter your details accurately

    Age, gender, height, and weight all affect your basal metabolic rate. Use your current weight, not your goal weight. Toggle between metric and imperial units as needed.

  2. Be honest about your activity level

    "Moderately active" means structured exercise 3–5 days per week. Walking to work and taking the stairs counts as "lightly active" at most. Overestimating activity is the most common error.

  3. Choose your goal

    Fat loss applies a percentage-based deficit (20% for males, 15% for females, capped at 500 cal/day). Muscle gain applies a modest surplus (10% males, 8% females). Both scale to your body size and gender. Maintenance keeps you at your TDEE.

  4. Use the result as a starting point

    Track your weight for 2–3 weeks. If you are not progressing toward your goal, adjust by 100–200 calories. No formula is perfect, but this gives you a reliable baseline.

The Mifflin-St Jeor Equation Explained

Mifflin-St Jeor Formula

Males: BMR = (10 × weightkg) + (6.25 × heightcm) − (5 × age) + 5

Females: BMR = (10 × weightkg) + (6.25 × heightcm) − (5 × age) − 161

TDEE = BMR × Activity Factor

The Mifflin-St Jeor equation (1990) is recommended by the Academy of Nutrition and Dietetics as the most accurate predictive equation for estimating basal metabolic rate in healthy adults. It accounts for the four primary variables that influence resting energy expenditure: body weight, height, age, and sex.

BMR vs. TDEE: Your basal metabolic rate (BMR) is the energy your body burns at complete rest, just to keep organs functioning, breathe, and maintain body temperature. Your total daily energy expenditure (TDEE) adds the calories burned through physical activity, non-exercise activity thermogenesis (NEAT), and the thermic effect of food.

Limitations: The Mifflin-St Jeor equation has a standard error of approximately 10%. It does not account for body composition (muscle-to-fat ratio), genetics, hormonal status, or metabolic adaptation. Very muscular individuals may underestimate, while those with higher body fat may overestimate. For the highest precision, indirect calorimetry (measuring oxygen consumption) provides a measured BMR.

Activity Level Factor Description
Sedentary 1.2 Desk job, little to no 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 Athlete or physical job + training

Frequently Asked Questions

What is the Mifflin-St Jeor equation?
The Mifflin-St Jeor equation (1990) estimates your basal metabolic rate using weight, height, age, and sex. The Academy of Nutrition and Dietetics considers it the most accurate predictive formula for the general population, more reliable than the older Harris-Benedict equation.
How many calories should I eat to lose weight?
This calculator uses a gender-aware percentage deficit (20% for males, 15% for females) capped at 500 cal/day. Women receive a smaller deficit because research shows they are more susceptible to hormonal disruption and RED-S at aggressive deficits. This targets 0.5–0.7% of bodyweight loss per week, the range that best preserves muscle mass.
How many calories do I need to build muscle?
This calculator uses a 10% surplus for males and 8% for females, since women gain muscle at roughly half the rate of men and a smaller surplus minimises unnecessary fat gain. Research shows larger surpluses do not produce more muscle, only more fat. Pair with a progressive resistance training program.
How accurate are calorie calculators?
The Mifflin-St Jeor equation has a standard error of about 10%, meaning your actual BMR could be 10% higher or lower. Use the result as a starting point, weigh yourself consistently for 2–3 weeks, and adjust by 100–200 calories if your weight is not trending in the expected direction.
Should I eat back calories burned during exercise?
The activity multiplier already accounts for your general exercise level. Eating back additional exercise calories on top of your TDEE often leads to overestimating intake. If you are doing significantly more activity than your selected level on a given day, a small additional 100–200 calorie increase is reasonable.

Related Reading & Tools

Learn more about daily protein targets

How much protein do you actually need per day?

How strength training supports fat loss

Why resistance training is essential during a caloric deficit.

Calculate your protein target

Science-based protein targets by weight, activity level, and goal.

All Tools

Browse all free fitness and nutrition calculators.