BMR Calculator
Find out how many calories your body burns doing absolutely nothing.
This BMR calculator estimates your basal metabolic rate — the calories your body burns at complete rest just keeping you alive: breathing, circulation, cell repair, and brain function. It uses the Mifflin-St Jeor equation, the current standard in clinical nutrition, and shows the result the instant your details are in.
BMR is the biggest single component of daily energy use, typically 60–70% of everything you burn. Knowing it explains a lot: why crash diets stall (your body is defending this baseline), why muscular people can eat more (muscle raises BMR), and why needs drift down slowly with age.
The calculation runs entirely in your browser — your height, weight, and age are never uploaded.
How to calculate your BMR
- Select your sex — the equation uses different constants for men and women.
- Enter your age in years.
- Enter your height and weight (metric or imperial, your choice).
- Read your BMR in calories per day — no button press needed, it appears live.
- To estimate total daily needs, multiply by an activity factor or use the calorie calculator.
The Mifflin-St Jeor equation
For men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5. For women: the same terms with −161 instead of +5. Published in 1990, it replaced the older Harris-Benedict formula after studies showed it tracks measured resting metabolism more closely in contemporary populations.
Remember that BMR is a resting floor, not a food target. Eating at or below BMR for long periods is not sustainable for most people; total daily needs are BMR multiplied by an activity factor between roughly 1.2 (sedentary) and 1.9 (very active).
What BMR does and doesn't include
BMR captures only the energy of staying alive at complete rest — organ function, breathing, circulation, temperature regulation, and cellular maintenance — measured after digestion, in a neutral-temperature room. It excludes any movement, exercise, or the calories spent digesting food.
Because it is a resting floor, BMR is always lower than what you actually burn in a day. It is the foundation you build a daily calorie estimate on, not a target in itself — a distinction that trips up people who try to eat "at their BMR".
A worked example
For a 40-year-old man, 180 cm, 82 kg: BMR = 10×82 + 6.25×180 − 5×40 + 5 = 820 + 1,125 − 200 + 5 = 1,750 calories a day. That is the energy his body would use lying still for 24 hours.
A woman of the same height, weight, and age uses the −161 constant: 820 + 1,125 − 200 − 161 = 1,584 calories. The 166-calorie gap comes entirely from the sex constant, reflecting average differences in body composition.
Turning BMR into daily needs
To estimate total daily energy expenditure (TDEE), multiply BMR by an activity factor: about 1.2 if sedentary, up to roughly 1.9 for those training intensely most days. The man above at 1,750 BMR would burn about 2,100 sedentary and around 2,700 if moderately active.
That multiplication is where a resting number becomes a food-planning number. If you want the calculator to do it for you, the calorie calculator applies the activity factor and adds weight-loss and weight-gain targets automatically.
What raises or lowers your BMR
BMR scales with body size and, importantly, lean mass — muscle is metabolically active, so more of it lifts your resting burn. That is why two people of the same weight can have different BMRs, and why resistance training gently raises the baseline over time.
It drifts down with age, roughly 1–2% per decade after early adulthood, partly from muscle loss. Sex, genetics, and thyroid function also matter, and extreme or prolonged dieting can suppress BMR temporarily as the body defends its energy stores.
Accuracy, assumptions, and limits
Mifflin-St Jeor is accurate to within about 10% for most adults, but it is a population formula — it cannot see your individual muscle mass, hormones, or medical conditions. Only indirect calorimetry, which measures your oxygen consumption in a lab, gives a truly personal figure.
The estimate is least reliable at the extremes: very muscular athletes, people with obesity, and the very lean or elderly. Treat the number as a solid starting point and refine it by tracking how your weight responds over a few weeks.
A note on health, and related tools
This is an educational estimate, not medical advice. If you are pregnant, managing a medical condition, or considering a very low-calorie diet, speak to a doctor or registered dietitian before acting on any calorie figure derived from your BMR.
BMR pairs naturally with two companions here: the calorie calculator turns it into daily targets, and the body fat calculator estimates the lean mass that partly drives the number in the first place. Together they give a fuller picture than any single metric.
Frequently asked questions
What exactly does BMR measure?
The energy your body uses at total rest in a neutral environment, after digestion is complete — the cost of basic life processes. Any movement, digestion, or exercise burns calories on top of it.
What is the difference between BMR and TDEE?
TDEE (total daily energy expenditure) is BMR plus everything else — activity, exercise, and the energy cost of digesting food. TDEE is what you actually burn in a normal day.
Should I eat at my BMR to lose weight?
Usually not. Since you burn more than BMR every day, eating slightly below your total daily expenditure creates a deficit while staying above BMR — a more sustainable approach for most people.
How accurate is a BMR formula?
Mifflin-St Jeor is accurate to within about 10% for most adults. Only indirect calorimetry (measuring your oxygen use in a lab) gives a truly individual figure.
Is this medical advice?
No — it is an educational estimate. If you are managing a medical condition, are pregnant, or are considering a very low-calorie diet, consult a doctor or registered dietitian first.
Why is my BMR lower than my friend's?
BMR scales with body size, muscle mass, age, and sex. More lean mass means a higher BMR, and it declines gradually with age — around 1–2% per decade after early adulthood.