Health
BMR Calculator
The equation predicts to within 10% of a measured rate. This page shows that band, because a single figure hides it.
What ageing does, next to what the equation does not know
Each row is the same person at a different age. The whole span from 20 to 60 moves the estimate by 200 kcal — less than the width of the range on any single row.
| Age | Basal metabolic rate | Lower end of the range | Upper end of the range |
|---|---|---|---|
| 20 | 1,390 | 1,251 | 1,529 |
| 30The figures above. | 1,340 | 1,206 | 1,474 |
| 40 | 1,290 | 1,161 | 1,419 |
| 50 | 1,240 | 1,116 | 1,364 |
| 60 | 1,190 | 1,071 | 1,309 |
The formula
Worked example
A 30-year-old woman, 165 cm, 62 kg
- 10 × 62 = 620
- 6.25 × 165 = 1,031.25
- 620 + 1,031.25 − 150 − 161 = 1,340 kcal a day at rest
- Within 10%: somewhere between 1,206 and 1,474
Where this goes wrong
Reading the number as if it were measured
This is a regression fitted to 498 people, not a measurement of you. The systematic review that recommends it found it predicts within 10% of a measured rate more often than any other common equation — which also means the band is 268 kcal wide in the example above, wider than the difference between being 30 and being 70. Anyone publishing a calorie target to the nearest kilocalorie from this equation is dressing up an estimate. The review also warns that older adults and US-residing ethnic minorities were underrepresented both in building these equations and in validating them.
Questions
- What is BMR?
- Basal metabolic rate is the energy your body uses doing nothing at all — breathing, circulating blood, maintaining temperature, repairing tissue. It is measured in a laboratory by indirect calorimetry after an overnight fast and complete rest. Everything you do on top of that is added separately.
- What is the difference between BMR and TDEE?
- BMR is the resting figure. TDEE — total daily energy expenditure — is that figure multiplied by an activity factor to cover everything you do awake. The multipliers people use (1.2 sedentary, 1.55 moderate, 1.9 very hard) do not come from the same research as the equation and have no comparable pedigree, which is why they are kept on a separate page rather than folded in here silently.
- Why only one equation, when other calculators offer three?
- Because offering a choice you cannot make is not a service. The Academy of Nutrition and Dietetics systematic review compared the four equations in common clinical use and found Mifflin–St Jeor the most reliable, predicting within 10% of measured in more people than any other and with the narrowest error range. Showing you three formulas and letting you pick moves the decision to whoever knows least about it.
- How accurate is this for me?
- The band on this page is the answer: within about 10%, most of the time. Body composition is the biggest thing the equation cannot see — two people of the same weight, height, age and sex can differ substantially in muscle mass, and muscle costs more energy at rest than fat does. Thyroid function, genetics and recent dieting all move it too.
- Does it work for older adults, or for everyone?
- Less well than for the population it was fitted to, and the review says so explicitly: older adults and US-residing ethnic minorities were underrepresented both in the development of these equations and in the studies validating them, and it advises a high level of suspicion about accuracy for those groups. That is a limitation of the research, not a detail of this page — but no other calculator seems to mention it.