How many calories do you burn a day? The Mifflin-St Jeor equation
To set a calorie deficit, you first need a rough idea of how many calories you burn in a day. You can estimate it in two steps:
- Work out the energy your body uses at rest.
- Multiply it by a factor for how active you are.
Step 1: your resting energy
Many calculators use an equation from a 1990 study by Mifflin, St Jeor and their colleagues. They measured the resting energy use of 498 healthy adults aged 19 to 78, then fitted an equation to the results. They also gave a simple form of it, one line for men and one for women:
Men: 10 × weight in kg + 6.25 × height in cm − 5 × age in years + 5
Women: 10 × weight in kg + 6.25 × height in cm − 5 × age in years − 161
The answer is in kilocalories a day, the unit food labels call calories. If you know your weight in pounds, divide it by 2.2046 to get kilograms. For height, multiply inches by 2.54 to get centimetres.
A worked example
A woman who is 35 years old, 165 cm tall and weighs 70 kg:
10 × 70 + 6.25 × 165 − 5 × 35 − 161
700 + 1,031 − 175 − 161 = about 1,395 kcal a day
A man who is 40 years old, 178 cm tall and weighs 85 kg:
10 × 85 + 6.25 × 178 − 5 × 40 + 5
850 + 1,113 − 200 + 5 = about 1,768 kcal a day
That is what each of them would burn lying still all day. Real days include moving, so the next step adds that.
Step 2: the activity factor
Many calculators multiply the resting figure by one of five factors:
| How active you are | Factor |
|---|---|
| Little or no exercise | 1.2 |
| Light exercise, 1 to 3 days a week | 1.375 |
| Moderate exercise, 3 to 5 days a week | 1.55 |
| Hard exercise, 6 to 7 days a week | 1.725 |
| Very hard exercise or a physical job | 1.9 |
The woman above walks to work and does yoga twice a week, so she picks 1.375:
1,395 × 1.375 = about 1,920 kcal a day
The man trains four times a week and picks 1.55:
1,768 × 1.55 = about 2,740 kcal a day
A word of honesty about this table. These five factors are a convention. They appear in calculator after calculator, but we could not trace them to any study that set them. A joint expert report on human energy needs from the FAO, WHO and UNU, published in 2004, uses three bands instead:
| Lifestyle | Physical activity level |
|---|---|
| Sedentary or light activity | 1.40 to 1.69 |
| Active or moderately active | 1.70 to 1.99 |
| Vigorous or vigorously active | 2.00 to 2.40 |
The lowest band there starts at 1.40, well above the 1.2 in the common table. So if you pick 1.2, you may be underestimating what you burn.
How close is the estimate?
It is a starting point, not a measurement. The equation describes the average person of your weight, height, age and sex. You may burn more or less than that, and the activity factor is a guess on top.
So use the estimate to start, then let your body correct it:
- Eat at the level you chose for three or four weeks.
- Follow your trend weight, not single weigh-ins.
- If the trend holds steady, you have found your real maintenance level. If it falls, you are eating below it.
As your weight changes, run the equation again. A lighter body uses less energy at rest, and the same activity costs it less. Downtrend reruns it as your trend weight changes, and sets the result beside the deficit your trend points to, so the estimate keeps up with you.
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. American Journal of Clinical Nutrition, 1990. The two equations are printed in the abstract.
- FAO, WHO and UNU. Human energy requirements. Report of a joint expert consultation, Rome, 2004. Table 5.3 gives the three bands.
- NIST. Handbook 44, Appendix C, 2026 edition. One pound is exactly 0.45359237 kg and one inch is exactly 2.54 cm.
This article is general information, not medical advice. Talk to a doctor before a big change to what you eat or how you train, and especially if you are pregnant, under 18 or have a health condition.