People often mix these up and then wonder why a diet built on their BMR leaves them exhausted. They answer different questions, and the second one is built on top of the first.
Side by side
| BMR | TDEE | |
|---|---|---|
| Stands for | Basal metabolic rate | Total daily energy expenditure |
| What it measures | Calories burned at complete rest: breathing, circulation, keeping warm | Everything BMR covers, plus digesting food, daily movement and exercise |
| How it is estimated | An equation from age, sex, height and weight | BMR multiplied by an activity factor |
| Typical use | A floor: the least your body needs | A starting point for how much to eat |
Where the BMR number comes from
Our BMR and TDEE Calculator uses the Mifflin-St Jeor equation, published in 1990 by Mifflin and colleagues in the American Journal of Clinical Nutrition (doi:10.1093/ajcn/51.2.241). They measured resting energy use in 498 healthy adults aged 19 to 78 and found that the older Harris-Benedict equation, from 1919, overestimated it by about 5%. The equation is: 10 × weight in kg + 6.25 × height in cm − 5 × age in years, then +5 for men or −161 for women.
A worked example
Take a 30-year-old woman, 165 cm tall and 60 kg. Her BMR is 10 × 60 + 6.25 × 165 − 5 × 30 − 161 = 1,320 kcal a day. Now apply the activity factors:
- Sedentary (× 1.2): about 1,584 kcal
- Light exercise 1 to 3 days a week (× 1.375): about 1,815 kcal
- Moderate exercise 3 to 5 days a week (× 1.55): about 2,046 kcal
The same body, the same BMR, and a gap of more than 700 kcal between “desk job” and “trains four times a week”. That gap is why TDEE, not BMR, is the figure for planning intake. Note that the activity factors are widely used rules of thumb, not measured values, which is one reason the result is an estimate.
Where people go wrong
- Eating at BMR. It is the energy for lying in bed all day. Eating that little while moving around usually just leaves you tired and hungry.
- Overrating activity. People tend to pick a higher activity level than they live. If in doubt, choose the lower one.
- Treating the result as exact. Both numbers are estimates and individual metabolism can differ by a few hundred calories either way.
When to use which
Use TDEE when you want a daily calorie target, and adjust it from your own results: weigh yourself under similar conditions for two to three weeks and nudge the target up or down. Use BMR when you only want to know the baseline cost of staying alive, for example to see why very low-calorie plans are hard to sustain.
These are general estimates, not medical or nutritional advice; talk to a doctor or dietitian if you have a health condition or are pregnant, and do not follow a very low calorie target without professional supervision.
Source: 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.