How does this calculation work?

Using basic demographic details like your age, sex, weight and height, we can estimate your total daily energy expenditure with validated equations (we use Mifflin-St Jeor, or Katch-McArdle if you know your body fat percentage). Your total energy expenditure is composed of four primary components:

• Basal metabolic rate (BMR): the energy your body uses at rest
• Non-exercise activity thermogenesis (NEAT): energy burned through activities associated with daily life, fidgeting, etc
• Thermic effect of food (TEF): energy burned through digestion, absorption, and storage of food
• Exercise: energy burned through physical activity

Mifflin-St Jeor is the most commonly-used BMR equation, and uses your weight, height, age, and sex to produce an estimate:

Katch-McArdle is a BMR equation that considers body fat percentage, and can be more accurate for people with very low or high body fat.

We use one of these equations to calculate the BMR, and then multiply by a factor that varies based on the level of activity you normally conduct. This activity factor includes the NEAT and TEF components as well (which tend to be less than 10% of your total energy expenditure) and on WHO activity levels.

The activity factor tends to vary between TDEE calculators: some will suggest that “no exercise” is equivalent to 1.2, but based on work conducted by other researchers, this seems too low.

How accurate is the estimate?

Several studies have compared the estimates of various formulas with experimentally-measured metabolic rates. The most accurate equation, the Mifflin-St Jeor, has been estimated to be within 10% of measured results, across both non-obese and obese individuals.