How to Calculate Daily Calorie Needs
Learn the Mifflin-St Jeor formula for BMR and TDEE to calculate your exact daily calorie needs based on weight, height, age, and activity level.
Understanding Your Basal Metabolic Rate (BMR)
Your Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest just to keep you alive — breathing, circulating blood, regulating temperature, and repairing cells. BMR typically accounts for 60-75% of your total daily energy expenditure, making it the foundation of any calorie calculation.
The most widely used and scientifically validated formula for estimating BMR is the Mifflin-St Jeor equation, published in 1990. It has been shown to be more accurate than older formulas like the Harris-Benedict equation for most people.
The Mifflin-St Jeor Formula
The formula uses your weight in kilograms, height in centimeters, and age in years:
- Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age(years) + 5
- Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age(years) − 161
Example Calculation
Let us calculate the BMR for a 30-year-old woman who weighs 65 kg and is 168 cm tall:
BMR = 10 × 65 + 6.25 × 168 − 5 × 30 − 161 = 650 + 1050 − 150 − 161 = 1,389 kcal/day
From BMR to TDEE: The Activity Multiplier
Your Total Daily Energy Expenditure (TDEE) is your BMR multiplied by an activity factor that accounts for physical movement throughout the day. TDEE represents the total number of calories you actually burn in a day.
The formula is simple: TDEE = BMR × Activity Multiplier
Activity Level Table
| Activity Level | Description | Multiplier |
|---|---|---|
| Sedentary | Desk job, little to no exercise | 1.2 |
| Lightly Active | Light exercise 1-3 days per week | 1.375 |
| Moderately Active | Moderate exercise 3-5 days per week | 1.55 |
| Very Active | Hard exercise 6-7 days per week | 1.725 |
| Extra Active | Athlete or very physical job + training | 1.9 |
Completing the Example
If our 30-year-old woman exercises moderately 3-5 days per week, her TDEE would be:
TDEE = 1,389 × 1.55 = 2,153 kcal/day
This means she needs approximately 2,153 calories per day to maintain her current weight. To lose weight, she would eat below this number; to gain weight, above it.
Important Considerations
- These formulas provide estimates. Individual metabolism can vary by 5-10% due to genetics, muscle mass, and hormonal factors.
- Recalculate your TDEE every 5-10 kg of weight change, as your BMR shifts with your body weight.
- If you are not seeing expected results after 2-3 weeks, adjust your calorie target by 100-200 kcal in the appropriate direction.
- A calorie tracking app can help you monitor intake against your calculated TDEE and make adjustments over time.