BMR calculator
Your basal metabolic rate is the energy your body uses just to keep you alive at rest. Enter your details to get it, plus the daily total once your activity is added on top.
Fill in your age, height and weight and your result appears here.
This is an estimate from a population equation, not a measurement of your metabolism. Individual rates vary by roughly 10 percent either side of the prediction, and more if you have a thyroid or metabolic condition.
The basics
What is BMR?
Basal metabolic rate is the energy your body spends doing nothing at all: keeping your heart beating, your lungs moving, your brain running, your temperature steady and your cells repairing themselves. It is measured in kilocalories per day, and for most adults it accounts for the largest single share of what they burn.
A true BMR is measured in a lab by indirect calorimetry, after an overnight fast, at rest, in a temperature-controlled room. Almost nobody has that number. What a calculator gives you instead is a prediction from an equation fitted to a population, using the four inputs that carry most of the signal: weight, height, age and sex.
That distinction matters more than it sounds. Your BMR is a real physiological quantity; the figure on this page is a statistical estimate of it. The two are usually close, and occasionally not.
How BMR is calculated
The calculator uses Mifflin-St Jeor and shows Harris-Benedict alongside it. Both are short enough to do by hand.
Mifflin-St Jeor (1990)
Men: BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age) + 5
Women: BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age) - 161
A woman of 35, 165 cm and 62 kg: 620 + 1031.25 - 175 - 161 = 1315 kcal per day. A man of 40, 180 cm and 80 kg: 800 + 1125 - 200 + 5 = 1730 kcal per day.
Revised Harris-Benedict (1984)
Men: BMR = 88.362 + (13.397 x kg) + (4.799 x cm) - (5.677 x age)
Women: BMR = 447.593 + (9.247 x kg) + (3.098 x cm) - (4.330 x age)
The same two people come out at 1381 and 1797 kcal per day, about 66 and 67 kcal above the Mifflin-St Jeor figures.
Mifflin-St Jeor is the one to trust where they differ. It was derived on a more contemporary sample and has repeatedly predicted measured resting energy expenditure more closely than Harris-Benedict, which is why dietetic practice moved to it. Harris-Benedict is shown because it is still what most calculators print, and a reader comparing two sites deserves to know why the numbers do not match.
From BMR to daily calories
BMR is what you burn at complete rest. Everything else you do adds to it. Multiplying by an activity factor gives total daily energy expenditure, the figure people usually actually want.
| Activity level | Multiplier | What it describes |
|---|---|---|
| Sedentary | x 1.2 | Desk job, little or no deliberate exercise |
| Lightly active | x 1.375 | Light exercise or sport 1 to 3 days a week |
| Moderately active | x 1.55 | Moderate exercise or sport 3 to 5 days a week |
| Very active | x 1.725 | Hard exercise 6 to 7 days a week |
| Extra active | x 1.9 | Hard daily training, or a physically demanding job on top of training |
The man in the example above, at a BMR of 1730 kcal and lightly active, works out at 1730 x 1.375 = 2379 kcal per day.
These multipliers are coarse by design. They lump together deliberate exercise, fidgeting, standing and the energy cost of digestion, all of which vary a lot between people who describe their week the same way. Treat the result as a starting point to test against what actually happens to your weight over a few weeks.
Read the number carefully
What a BMR estimate does not tell you
The equation is doing a lot of work with four inputs. Four things it cannot see are worth knowing before you plan anything around the result.
It is a prediction, not a measurement
Validation studies of Mifflin-St Jeor typically find it lands within 10 percent of measured resting energy expenditure for most people, which still means a plausible spread of a couple of hundred kilocalories a day on a figure near 1700. If you are planning around the number, plan around a range.
It cannot see your body composition
Muscle burns more at rest than fat does, but the equation only knows your total weight. Two people of the same age, height, weight and sex with very different amounts of muscle get an identical estimate, and the more muscular one is being underestimated. This is the gap the Katch-McArdle equation tries to close by taking lean body mass instead, which requires actually measuring your body composition.
It assumes an untroubled metabolism
An underactive or overactive thyroid shifts resting energy expenditure well outside what the equation predicts, and so can some medications. A sustained calorie deficit also lowers it, partly beyond what the weight loss alone explains, which is one reason a figure that fitted you last year may not fit you now.
It was derived on binary sex categories
Both equations carry a single sex term standing in for average differences in body composition. That makes them a poor fit for anyone those averages do not describe, including people on hormone therapy. Where it matters clinically, a measured resting energy expenditure or a body-composition-based equation is the better route, and worth raising with a doctor.
Beyond the estimate
What actually moves your resting rate
If the number has prompted you to look further, these are the things that genuinely shift resting energy expenditure, and the ones worth measuring rather than estimating.
Muscle mass
The single largest lever you have any control over. Building and keeping muscle raises resting expenditure and improves how your body handles glucose. Imaging measures how much you have and whether it is being infiltrated by fat, which weight alone cannot show.
Thyroid function
TSH, free T4 and free T3 are the direct read on the system that sets your metabolic pace. A rate that feels wrong for your build and habits is one of the more common reasons to check them.
Metabolic markers
Fasting glucose, HbA1c, insulin and triglycerides describe how efficiently you are handling the energy you take in. They move well before body weight does, in either direction.
Change over time
One estimate tells you very little. The same measurements repeated across a year tell you whether what you are doing is working, which is the only question the first number was ever standing in for.
Ahead Health membership
An equation guessed your metabolism. A membership measures it.
An Ahead Health membership is a year of structured prevention: repeat blood panels including thyroid and metabolic markers, a personal report you can actually read, and a prevention team that goes through it with you. It answers with measurements the question this calculator can only estimate.
Cancel before renewal. Your data stays yours and is never sold.
- Up to four blood check-ups a year, 80 plus biomarkers each
- Thyroid and metabolic markers, not just a weight trend
- A personal report reviewed by Swiss physicians
- Muscle and body composition from MRI, at member rates
- Your results tracked side by side, year over year
BMR questions, answered
Other calculators
Free tools that ask a different question about the same body.
This calculator provides general health information and is not a medical diagnosis. It does not replace an assessment by a doctor, and it is not a nutrition plan. If you are concerned about your metabolism, your weight or your energy levels, speak to a physician.