Mifflin-St Jeor BMR Calculator
Basal metabolic rate by the current standard equation
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Working out basal metabolic rate by the current standard equation is easier with Mifflin-St Jeor BMR Calculator, which answers as you type. Fill in Weight (kg), Height (cm) and Age (years) on Mifflin-St Jeor BMR and read your answer immediately. Nothing in Mifflin-St Jeor BMR is a black box. Anyone comparing options in Health can use Mifflin-St Jeor BMR to compare scenarios. You can disconnect once Mifflin-St Jeor BMR has loaded; the arithmetic runs locally. Mifflin-St Jeor BMR sits in the Health section next to free online mifflin-st jeor bmr calculator and mifflin st jeor bmr calculator basal metabolic rate. Mifflin-St Jeor BMR is great for comparing scenarios. Change one value and watch. Mifflin-St Jeor BMR stays bookmarked for next time.
Mifflin-St Jeor BMR: your daily calorie baseline
BMR is the energy you would burn lying still all day, and Mifflin-St Jeor is the equation the Academy of Nutrition and Dietetics rates most accurate for healthy adults. It is 10 × weight in kilograms, plus 6.25 × height in centimetres, minus 5 × age, then plus 5 for men or minus 161 for women.
BMR is the floor, not the budget. It is what your body spends staying alive: breathing, circulating blood, maintaining temperature and rebuilding tissue. Everything above it — walking to the kitchen, digesting lunch, a training session — is added on top, which is why the extra line shows a total daily figure at moderate activity.
The equation this calculator runs
This page uses the Mifflin-St Jeor equation, and naming it matters: pages on this SERP return different numbers for the same person because they run different equations (Harris-Benedict and Katch-McArdle are the usual alternatives) without always saying which one is in use.
BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5 — men
BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161 — women
Worked example: 80 kg, 180 cm, age 40, male → 800 + 1,125 − 200 + 5 = 1,730 kcal/day. Run the identical inputs as female and the answer is 800 + 1,125 − 200 − 161 = 1,320 kcal/day; the 166 kcal gap is the sex term and nothing else.
| Input | Term in the equation | Value |
|---|---|---|
| Weight 80 kg | 10 × 80 | 800 |
| Height 180 cm | 6.25 × 180 | 1,125 |
| Age 40 | − 5 × 40 | − 200 |
| Sex (male) | + 5 | + 5 |
| Total | BMR | 1,730 kcal/day |
From BMR to a daily total
BMR is the resting figure. Multiplying it by an activity factor turns it into a daily energy estimate (TDEE), and that factor is the only judgement in the chain — the default view on the calculator uses moderate:
| Activity level | Factor | At a 1,730 kcal BMR | At a 1,320 kcal BMR |
|---|---|---|---|
| Sedentary | 1.2 | 2,076 | 1,584 |
| Light | 1.375 | 2,379 | 1,815 |
| Moderate (calculator default) | 1.55 | 2,682 | 2,046 |
| Very active | 1.725 | 2,984 | 2,277 |
| Extra active | 1.9 | 3,287 | 2,508 |
Feed the same four inputs through the same equation and the answer is identical every time — the only guarantee a four-input estimate can offer.
What this page does not do
It is arithmetic on four inputs: weight, height, age and sex. It does not diagnose anything, it cannot know about thyroid conditions, medication, pregnancy or body composition, and it does not say how much anyone should eat. Questions in those areas — including the ones search engines show beside this query — need a clinician who has the history, not a formula with four variables. Muscle mass is the clearest internal limit: the equation reads weight, not what the weight is made of, so a very muscular person and a person of the same weight with more fat get identical output.
Related: body fat calculator, calorie deficit calculator and health calculators.
The equation, term by term
Mifflin-St Jeor is a straight-line estimate: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age(years) + s, where s is +5 for men and −161 for women.
Read the coefficients as what they measure. Weight contributes 10 kcal per kilogram — the largest single term, because lean and fat mass both cost energy to maintain. Height contributes 6.25 kcal per centimetre, a proxy for total body surface area. Age subtracts 5 kcal per year, reflecting the slow loss of lean mass that comes with it. The sex constant is not a judgement about size; it captures the average difference in body composition between men and women at the same height and weight.
Worked example: 70 kg, 170 cm, 30 years, male
Weight term: 10 × 70 = 700 kcal.
Height term: 6.25 × 170 = 1,062.5 kcal.
Age term: 5 × 30 = 150 kcal, subtracted.
Sex constant: +5.
700 + 1,062.5 − 150 + 5 = 1,617.5, which the page reports as 1,618 kcal/day. The same person entered as female gives 1,617.5 − 166 = 1,451.5 kcal/day, because the constant moves from +5 to −161.
From BMR to a daily calorie target
Multiply by an activity factor: 1.2 for desk work with little movement, 1.375 for light exercise a few days a week, 1.55 for moderate training, 1.725 for hard daily training, 1.9 for physical work plus training. The defaults at 1.55 give about 2,507 kcal/day.
Treat the multipliers as brackets, not measurements. Two people with identical BMR can differ by several hundred calories a day in genuine expenditure, and the scale over three weeks is a better arbiter than any factor.
Where the estimate drifts
Mifflin-St Jeor was derived from a modern population and predicts measured BMR within about 10% for most adults, but it systematically overestimates very lean, heavily muscled people (muscle is metabolically expensive but the equation cannot see it) and underestimates some older adults. A very low-calorie intake also lowers measured BMR below the prediction, because the body down-regulates rather than burning the calculated figure.
Mistakes worth avoiding
- Using BMR as a calorie target. Eating at BMR is a large deficit for an active person and a maintenance level for nobody.
- Entering weight in pounds. The field reads kilograms; 154 lb entered as 154 kg inflates BMR by roughly 1,100 kcal.
- Leaving sex at the default. The constant alone moves the answer by 166 kcal, which is larger than most people's intended deficit.
- Re-running monthly and expecting change. The equation responds to weight, height and age — not to how you feel or how much you trained this week.
What it cannot tell you
BMR says nothing about body composition, thyroid function, medication effects, pregnancy or illness, and it is not a diagnosis of a "slow metabolism". If measured expenditure and predicted BMR disagree by more than about 15%, that gap is worth raising with a clinician rather than adjusting the calculator.
Frequently Asked Questions
Is Mifflin-St Jeor better than Harris-Benedict?
For most adults, yes — it predicts measured resting energy expenditure more accurately, which is why dietetic bodies recommend it. Harris-Benedict tends to run high by roughly 5%, and the 1984 revision narrowed but did not close that gap.
Why does the female result drop by 166 kcal?
The sex constant changes from +5 to −161, a 166 kcal difference at identical weight, height and age. It reflects the average body-composition difference in the population the equation was fitted to, not an individual prediction.
Should I eat my BMR plus exercise calories?
Start from the activity multiplier total (BMR × 1.2–1.9), not from BMR plus a per-workout number. Per-exercise estimates double-count the movement already inside the multiplier and typically overstate the burn.
How accurate is 1,618 kcal/day for the defaults?
Within about 10% for a typical adult of that size — so roughly 1,460–1,780 kcal/day. The true figure depends on lean mass, which the equation cannot see, so treat a single number as a centre point rather than a measurement.
Does the 6.25 × height term make tall people burn much more?
It adds 6.25 kcal per centimetre, so 20 cm of extra height is 125 kcal/day. That is real but modest next to weight, where 10 kg is 100 kcal/day and body composition changes the true value far more than either term.
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