BMR vs TDEE: what each number means and how they differ

BMR and TDEE are both calorie estimates, but they measure very different things. BMR is what your body burns at complete rest. TDEE adds everything else — walking, thinking, digesting, exercising — over the course of a day. The gap between them is why two people of identical weight and height can have very different maintenance needs.

What BMR actually measures

BMR (Basal Metabolic Rate) is the energy required to keep your vital organs functioning while you lie still and fast. It is roughly:

Heart beating and lungs breathing
Brain and nervous system activity
Liver and kidney processing
Cellular repair and growth (at rest)

The BMR calculator estimates this using theMifflin-St Jeor equation, which takes your age, sex, height, and weight. For men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5. For women: the same, minus 161.

BMR typically accounts for 60–75% of total daily energy expenditure. The rest comes from activity and digestion.

What TDEE adds on top

TDEE (Total Daily Energy Expenditure) = BMR × activity factor. The activity factor ranges from 1.2 (sedentary) to 1.9 (very active). Use the TDEE calculator to see the full range:

Activity factors and their multipliers
Activity level	Multiplier	Typical week
Sedentary	1.2	Little or no exercise
Lightly active	1.375	Light exercise 1–3 days
Moderately active	1.55	Moderate exercise 3–5 days
Very active	1.725	Hard exercise 6–7 days
Extra active	1.9	Very hard exercise, or a physical job

When BMR and TDEE diverge

Two people who are the same age, sex, height, and weight will have the same BMR but very different TDEEs if one has a desk job and the other trains six days a week. The activity factor is the weak link: it is a five-step scale that cannot distinguish nuances within each band.

This is why the BMR calculator exists as its own tool. If you want to understand your baseline metabolism without the noise of your activity level, BMR isolates it. If you want to know what you actually burn in a day, TDEE is the number that matters for eating targets.

Katch-McArdle: a third option

The BMR calculator also offers the Katch-McArdle formula when you enter a body-fat percentage: BMR = 370 + (21.6 × lean mass in kg). Because it uses lean mass instead of total weight, it can be more accurate for people with an unusual body-fat percentage — but it inherits whatever error your body-fat estimate carries.

Formulas are estimates, not medical advice.

Sources

Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241-247.
Used for: Basal metabolic rate from weight, height, age and sex — the foundation of the TDEE and calorie-target calculators.
Katch VL, McArdle TD. Nutrition, exercise and energy expenditure. In: Exercise Physiology: Nutrition, Energy, and Body Composition. 2nd ed. Human Kinetics; 1993.
Used for: The Katch-McArdle BMR formula (370 + 21.6 x lean mass in kg), used as an alternative to Mifflin-St Jeor when body fat percentage is known.