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BMR: The Formula Behind Your Resting Calorie Burn
Health · 6 min read · Last updated September 2026
The Mifflin-St Jeor formula
Women: 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161
Worked example — 80 kg, 180 cm, 30-year-old male: 10 × 80 = 800; 6.25 × 180 = 1,125; 5 × 30 = 150. So 800 + 1,125 − 150 + 5 = 1,780 kcal/day.
From BMR to daily needs (TDEE)
| Activity level | Multiplier | Same man's TDEE |
|---|---|---|
| Sedentary (desk job) | × 1.2 | 2,136 kcal |
| Lightly active | × 1.375 | 2,448 kcal |
| Moderately active | × 1.55 | 2,759 kcal |
| Very active | × 1.725 | 3,071 kcal |
The multiplier you pick moves the answer more than any formula choice — a sedentary vs very-active pick spans 900+ kcal. Calibrate honestly: most desk workers are 1.2–1.375 even with gym visits.
Why BMR formulas disagree
The older Harris-Benedict equation gives 1,854 kcal for the same man — 74 kcal higher than Mifflin. Neither is "wrong": both are population regressions with real scatter (roughly ±200 kcal for any individual). Mifflin is preferred today because it tracks measured values somewhat better in modern populations.
Try the calculators
Worked example: BMR Calculator at its default inputs
Open BMR Calculator and press calculate without editing a field. What comes back is the table and result below, so the bmr numbers here are checkable in one click.
| Input | Default |
|---|---|
| Weight (kg) | 70 |
| Height (cm) | 170 |
| Age | 30 |
| Body Fat % (for Katch-McArdle) | 15 |
Result: BMR: 1618 cal/day (Mifflin-St Jeor)
The steps behind that answer
- Formula (Mifflin-St Jeor, 1990):
- Male: BMR = 10W + 6.25H - 5A + 5
- Female: BMR = 10W + 6.25H - 5A - 161
- ≈ 1618 cal/day
Weight (kg): half, as given, and half again
The table below varies weight (kg) alone — half, the default, and half again.
| Weight (kg) | Result |
|---|---|
| 35 | BMR: 1268 cal/day (Mifflin-St Jeor) |
| 70 | BMR: 1618 cal/day (Mifflin-St Jeor) |
| 105 | BMR: 1968 cal/day (Mifflin-St Jeor) |
Read the three rows as a range: the spread between them is how much the answer depends on weight (kg) alone, with everything else held still.
Related guides
BMR is a resting measurement
Basal metabolic rate is the energy needed at complete rest to keep organs running. Predictive equations estimate it from weight, height, age and sex, and they carry an error of roughly 10% against measured values in an individual.
That error is why the first two weeks of any calorie plan are a test rather than a prescription. Use the estimate as a starting point, then adjust based on what the scale and your energy levels actually do.
Activity multipliers are the weak link
Total daily energy is BMR times an activity factor. The factor is a coarse category, and people routinely choose one that is too high: an office job with three gym sessions is not the same as a job on your feet all day.
If your weight is stable, you already know your maintenance calories empirically. That number beats any multiplier, and it is easy to estimate from two weeks of intake and weight change.
Muscle, age and the direction of drift
BMR falls with age partly because muscle mass falls, and it rises with muscle mass independently of exercise during the measurement. Resistance training changes body composition and, over years, the resting burn.
Crash dieting lowers it too, through lost muscle and adaptive thermogenesis. That is why the same calorie intake stops producing loss after a long deficit, and why a diet break or a slower rate is often the better move.
Frequently asked questions
How is BMR calculated?
The standard Mifflin-St Jeor formula: 10 × weight in kg + 6.25 × height in cm − 5 × age, plus 5 for men or minus 161 for women. For an 80 kg, 180 cm, 30-year-old man that is 1,780 kcal/day.
What is a good BMR for my age?
BMR declines roughly 5 kcal per year of age in the formula (the −5 × age term). Typical adult values fall between about 1,200 and 1,900 kcal/day depending on size, sex and age — there is no single "good" number.
Should I eat my BMR to lose weight?
No. BMR is your burn at complete rest; total daily needs (BMR × activity factor) are the relevant baseline. Eating at or below BMR while active creates an unnecessarily aggressive deficit for most people.
Why do BMR and TDEE calculators give different numbers?
Different equations (Mifflin vs Harris-Benedict) and different activity multipliers. The multiplier choice usually moves the total more than the equation does — pick your activity level honestly.
What do I do with my BMR once I have it?
Multiply it by an activity factor to get your daily burn, then set your intake against that number. The ideal weight guide covers what a sensible target weight looks like, and the BMI guide explains the screening number most people pair with BMR.
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