Calorie Calculator
Calculate your daily calorie needs using the Mifflin-St Jeor formula.
What is a Calorie Calculator?
A calorie calculator estimates how much energy your body needs each day to maintain, lose, or gain weight. It combines two concepts: your Basal Metabolic Rate (BMR) – the energy required at complete rest for breathing, circulation, cell repair, and organ function – and your activity level, which together determine your Total Daily Energy Expenditure (TDEE). Understanding your TDEE is the foundation of any evidence-based nutrition plan, whether your goal is fat loss, muscle gain, athletic performance, or simply eating intuitively with more confidence.
This tool uses the Mifflin-St Jeor equation, which the Academy of Nutrition and Dietetics considers the most reliable predictive formula for healthy adults. It was developed in 1990 using measured resting metabolic rates and has since replaced the older Harris-Benedict equation in most clinical settings. The formula incorporates weight, height, age, and sex to produce a BMR estimate with an average error margin of roughly 10%, which is accurate enough for the vast majority of practical nutrition planning.
Once BMR is known, TDEE is calculated by multiplying it with an activity factor that reflects how much movement you perform on a typical day. A sedentary office worker has very different needs from a construction worker or competitive athlete, and ignoring this multiplier is one of the most common reasons calorie targets fail in practice.
How is it Calculated?
The Mifflin-St Jeor BMR formula is:
- Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age(y) + 5
- Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age(y) − 161
TDEE = BMR × activity factor. Common activity factors are 1.2 (sedentary), 1.375 (light exercise 1–3 days/week), 1.55 (moderate 3–5 days/week), 1.725 (hard 6–7 days/week), and 1.9 (very hard physical job or twice-daily training).
Worked example:A 30-year-old woman who is 165 cm tall and weighs 65 kg with a moderate activity level. BMR = 10 × 65 + 6.25 × 165 − 5 × 30 − 161 = 650 + 1031.25 − 150 − 161 = 1370 kcal. TDEE = 1370 × 1.55 ≈ 2124 kcal/day to maintain weight. A 500 kcal deficit (~1624 kcal) would target roughly 0.5 kg per week of fat loss.
Key Facts & Tips
- 1 kg of body fat stores roughly 7700 kcal, so a daily 500 kcal deficit produces about 0.45–0.5 kg of loss per week.
- Never drop below 1200 kcal/day (women) or 1500 kcal/day (men) without medical supervision.
- Protein intake of 1.6–2.2 g/kg body weight helps preserve lean mass during a deficit.
- Recalculate TDEE every 4–6 weeks; as body weight changes, so do energy needs.
- Sleep, stress, and hydration measurably influence appetite and metabolic output.
Frequently Asked Questions
How many calories should I eat per day to lose weight?
A sustainable deficit of 500 kcal below your TDEE typically produces about 0.45 kg (1 lb) of weight loss per week. Deficits larger than 1000 kcal risk muscle loss and nutrient deficiencies.
What is the difference between BMR and TDEE?
BMR is the energy your body burns at complete rest. TDEE is BMR multiplied by an activity factor to include daily movement, exercise, and the thermic effect of food.
Is the Mifflin-St Jeor formula accurate?
It is considered one of the most accurate predictive BMR equations for healthy adults, with an average error of around 10%. Individual variation still exists.
Do I need to count calories to stay healthy?
Not necessarily. Counting is useful for specific goals, but many people maintain a healthy weight through whole foods, portion control, and regular activity.
Why does my calorie requirement decrease with age?
Lean muscle mass declines and hormonal changes slow metabolism. TDEE drops roughly 1–2% per decade after age 20; strength training helps offset this.