How the TDEE Formula Works
The TDEE formula combines two components: your Basal Metabolic Rate (BMR) and an activity multiplier. BMR represents the calories your body burns at complete rest — keeping your heart beating, lungs breathing, and cells functioning. The activity multiplier then scales this number based on how physically active you are throughout the day.
The most widely used and research-backed equation for calculating BMR is the Mifflin-St Jeor formula, which has been shown to predict resting metabolic rate within 10% accuracy for most healthy adults.
The Mifflin-St Jeor Equation
For men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + 5
For women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) − 161
Once you have your BMR, multiply it by the appropriate activity factor to get your TDEE. For example, a moderately active person would multiply their BMR by 1.55.
Other TDEE Formulas
While Mifflin-St Jeor is the default in most modern calculators, other formulas exist. The Harris-Benedict equation, developed in 1919 and revised in 1984, was the standard for decades but tends to overestimate calorie needs slightly. The Katch-McArdle formula factors in lean body mass, making it more accurate for people who know their body fat percentage — particularly athletes and very lean or very overweight individuals.
Each formula has trade-offs. Mifflin-St Jeor offers the best balance of accuracy and simplicity for the general population. If you have access to a body fat measurement, the Katch-McArdle formula may give you a more personalised result. Our calculator uses Mifflin-St Jeor by default, with the option to input body fat percentage for enhanced precision.
Why No Formula Is Perfect
All TDEE formulas are estimates based on population averages. Individual variation in metabolism, Non-Exercise Activity Thermogenesis (NEAT), the thermic effect of food, and genetics mean your actual energy expenditure may differ by 5–15%. Use your calculated TDEE as a starting point and adjust based on real-world results over 2–4 weeks.