The Mifflin-St Jeor equation estimates how many calories your body burns at rest. For men it is (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5; for women the same three terms finish − 161 instead. Published in 1990, it is the formula behind this site's BMR calculator, and a later systematic review found it the most reliable of the commonly used equations.
The equation, both versions
| Version | Formula |
|---|---|
| Men | (10 × kg) + (6.25 × cm) − (5 × age) + 5 |
| Women | (10 × kg) + (6.25 × cm) − (5 × age) − 161 |
Weight in kilograms, height in centimetres, age in whole years. The answer is calories per day.
Every term is identical between the two versions except the final constant, which is the only place sex enters. That single difference is worth a section of its own, further down.
If you think in pounds and inches, convert before you start: divide pounds by 2.2046 for kilograms, multiply inches by 2.54 for centimetres. Someone who is 190 lb and 6 ft 0 in tall is 86.18 kg and 182.9 cm.
Worked by hand
Take a 30-year-old man weighing 80 kg at 178 cm. Working through the four terms in order:
- 10 × 80 kg = 800
- 6.25 × 178 cm = 1,112.5
- 5 × 30 years = 150
- 800 + 1,112.5 − 150 + 5 = 1,767.5, which rounds to 1,768 calories a day
Now a 35-year-old woman weighing 65 kg at 165 cm, using the same steps with the female constant: 650 + 1,031.25 − 175 − 161 = 1,345.25, or 1,345 calories a day.
Both figures reproduce exactly what our BMR calculator returns for the same inputs, because that page runs this arithmetic and nothing else. If you get a different answer, the discrepancy is in the working rather than in the tool.
It estimates resting energy expenditure — not, strictly, basal metabolic rate
This is the detail almost every page describing the formula gets wrong, including, until recently, some of the wording on this site.
The equation is universally described as a BMR equation. The paper that introduced it does not use that term. Mifflin, St Jeor and colleagues wrote about resting energy expenditure (REE) throughout, and their measurements were made by indirect calorimetry under resting conditions. Basal metabolic rate is a stricter idea: measured after an overnight fast, immediately on waking, at complete rest in a thermally neutral room. Resting energy expenditure is measured under less restrictive conditions and is consequently the slightly larger number.
How much larger is not something this equation can tell you, and you should be wary of pages that put a confident percentage on it, because the 1990 paper does not measure the gap. What matters practically is smaller than the terminology suggests: the difference does not change how the figure is used, since the next step multiplies it by an activity factor that carries far more uncertainty than the BMR-versus-REE distinction does.
The 166-calorie gap between the two constants
The male version ends +5 and the female version −161, a difference of exactly 166 calories. It is often explained as the equation's allowance for differences in body composition between men and women of the same height, weight and age.
That reading is reasonable, but it is interpretation rather than something the paper claims. In the published regression, sex enters as a plain indicator variable with a coefficient of 166 — the model does not attribute that number to body composition or to anything else. Indeed the authors reported fat-free mass separately, and found it the single strongest predictor of resting energy expenditure they tested, explaining about 64% of the variance on its own.
Which points at the equation's real limitation. Fat-free mass predicts resting metabolism better than height, weight and age do — and fat-free mass is precisely what the equation does not ask you for. It infers an average body composition from your size and sex, then applies a fixed correction. For anyone whose composition is not average, the estimate inherits that error. If you know your body fat percentage, the lean body mass calculator gives the figure the research says matters most.
Turning the result into a daily calorie figure
Resting energy expenditure is what you burn doing nothing. To reach a daily total, it is conventionally multiplied by an activity factor:
| Activity level | Multiplier | Example man (1,768) |
|---|---|---|
| Sedentary (little or no exercise) | 1.2 | 2,122 |
| Light (1–3 days a week) | 1.375 | 2,431 |
| Moderate (3–5 days a week) | 1.55 | 2,740 |
| Active (6–7 days a week) | 1.725 | 3,050 |
| Very active (physical job, or twice daily) | 1.9 | 3,359 |
Computed from the rounded 1,768, which is the figure the calculator displays — so multiplying the number you can see reproduces the column exactly. Our TDEE calculator performs this step.
These multipliers are a long-standing convention rather than a research finding, and it is worth knowing that a more formal framework exists and does not agree with them. The FAO/WHO/UNU report Human Energy Requirements expresses habitual daily energy as a physical activity level, or PAL, and places a sedentary or light activity lifestyle at 1.40–1.69, an active or moderately active lifestyle at 1.70–1.99, and a vigorous or vigorously active lifestyle at 2.00–2.40, noting that values above 2.40 are difficult to sustain.
Set those side by side and the mismatch is obvious: the conventional ladder's sedentary multiplier of 1.2 sits below the bottom of FAO's entire lowest band. The two systems are not measuring quite the same thing — PAL is defined against basal metabolic rate and derived from population energy-expenditure data — but the practical lesson stands. The activity step is the loosest part of the whole calculation, and it is where most of the error in a daily calorie estimate comes from.
How accurate is it?
Better than the alternatives, and still not precise for any one person.
A systematic review by Frankenfield, Roth-Yousey and Compher, published by the American Dietetic Association in 2005, compared the common predictive equations against measured resting metabolic rate in both non-obese and obese adults. It concluded that Mifflin-St Jeor was the most reliable, predicting RMR within 10% of the measured value in more individuals than any other equation tested, and with the narrowest error range. That review is the reason the equation became the default in dietetic practice.
The same review is careful about what that does not mean. It notes that “noteworthy errors and limitations exist when it is applied to individuals and possibly when it is generalized to certain age and ethnic groups.” Being the best available equation and being accurate for you are different claims.
The 1990 paper made a related point about its predecessor. The Harris-Benedict equations, derived in 1919, overestimated measured resting energy expenditure by 5% in Mifflin's sample — a systematic bias in a formula that had been in use for seventy years by that point.
What the sample was, and what follows from it
The equation was derived from 498 healthy adults: 247 women and 251 men, aged 19 to 78, of whom 264 were of normal weight and 234 were obese. Resting energy expenditure was measured by indirect calorimetry rather than estimated.
Two things follow. The inclusion of a large obese subgroup is a genuine strength, and part of why the equation holds up better than Harris-Benedict across body sizes. But the sample was healthy adults, so the equation carries no claim about people with conditions that alter metabolic rate, and it says nothing about children.
In practice the estimate is best treated as a starting point rather than a measurement. The usual approach is to take the figure, hold intake near the corresponding target for a few weeks, and watch the weight trend rather than daily readings — which shows how far the estimate was off for you specifically. Our calorie deficit calculator turns the result into a target, and the weight-loss timeline calculator projects it forward at a steady rate and flags whether that pace is a sensible one.
This guide is general information, not medical advice. Predictive equations estimate averages and carry meaningful error for individuals; they cannot tell you what you personally should eat. Speak with a qualified healthcare professional, such as a registered dietitian, about your own circumstances.
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;51(2):241–247; Frankenfield D, Roth-Yousey L, Compher C, “Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review,” Journal of the American Dietetic Association 2005;105(5):775–789; FAO/WHO/UNU, Human Energy Requirements — Chapter 5, Physical activity level (PAL) categories.