BMR & TDEE calculator
Resting metabolic rate by three published equations, plus total daily energy expenditure.
Enter a weight above zero.
Basal metabolic rate, total daily energy expenditure, and why the equations disagree
Basal metabolic rate is what your body spends staying alive at complete rest — running your brain, heart, kidneys and the constant turnover of tissue. It is the largest single component of what you burn in a day, usually 60 to 70 per cent of it, and it is the number every calorie target is built on top of.
Total daily energy expenditure is BMR multiplied by an activity factor. That multiplication is where most of the error comes in: the factors are coarse bands, and "moderately active" means different things to different people. The equations themselves are regressions fitted to study populations, so even a perfect input gives you the average for people shaped like you, not your number.
Formulas
Worked examples
| Person | Mifflin-St Jeor | Harris-Benedict | TDEE, moderate |
|---|---|---|---|
| M, 30, 80 kg, 180 cm | 1780 kcal | 1854 kcal | 2759 kcal |
| F, 30, 65 kg, 165 cm | 1370 kcal | 1430 kcal | 2124 kcal |
| M, 55, 95 kg, 175 cm | 1774 kcal | 1889 kcal | 2749 kcal |
| F, 22, 52 kg, 158 cm | 1237 kcal | 1323 kcal | 1917 kcal |
The two equations rarely agree exactly. Where they differ by more than about 100 kcal, neither is more right — the spread is the honest error bar.
Activity multipliers
| Level | Factor | Roughly means |
|---|---|---|
| Sedentary | 1.2 | Desk work, no deliberate exercise |
| Lightly active | 1.375 | Exercise 1-3 days a week |
| Moderately active | 1.55 | Exercise 3-5 days a week |
| Very active | 1.725 | Hard exercise 6-7 days a week |
| Extra active | 1.9 | Physical job, or training twice a day |
These bands are conventional rather than derived. The jump from sedentary to extra active is a 58% swing, so an optimistic self-assessment costs more than any difference between the equations.
Worth knowing
- Mifflin-St Jeor is the usual default. It was fitted more recently than Harris-Benedict and on a population closer to a modern one, and it predicts measured resting expenditure more accurately in most comparisons.
- There are two Harris-Benedict equations and they are constantly confused. The 1919 original and the 1984 Roza-Shizgal revision use different coefficients and give answers tens of kilocalories apart. This tool uses the revision.
- Katch-McArdle is the most accurate of the three when body fat is genuinely known, and the least usable when it is not — a guessed body fat percentage makes it worse than the equations that never asked.
- Individual resting rates vary by roughly 200 kcal a day around any of these predictions, even after accounting for weight, height, age and sex. Treat the output as a starting point to adjust from over a few weeks.
Frequently asked questions
- Which BMR formula should I use?
- Mifflin-St Jeor unless you have a measured body fat percentage, in which case Katch-McArdle. Mifflin was fitted more recently and on a more representative population than Harris-Benedict, and it predicts measured resting expenditure better in most published comparisons.
- What is the difference between BMR and TDEE?
- BMR is what you burn at complete rest, keeping your organs running and your tissue turning over. TDEE adds everything else — moving around, digesting food, exercising. TDEE is BMR multiplied by an activity factor between 1.2 and 1.9, so it is always the larger number and always the more approximate one.
- Why do two calculators give me different numbers?
- Almost always because they use different equations, or the same equation from a different year. Mifflin-St Jeor, the 1919 Harris-Benedict and its 1984 revision all give different answers for the same person, and many sites do not say which one they are running.
- How accurate is a calculated BMR?
- Within about 10 per cent for most people, which on a 1,800 kcal basal rate is a spread of nearly 200 kcal a day. That is enough to matter over months. The practical approach is to use the estimate as a starting point, track actual weight change for two to three weeks, and adjust from what really happened.