BMR Calculator
This free BMR calculator estimates your Basal Metabolic Rate, the calories your body burns at rest, just to keep you alive. Enter your details below to find your number and learn exactly what it means for your goals.
What is BMR?
Your Basal Metabolic Rate (BMR) is the number of calories your body burns just to stay alive while you are completely at rest. Even if you spent an entire day lying still in bed, your body would still spend energy breathing, pumping blood, growing and repairing cells, and keeping your brain and organs running. That baseline energy cost is your BMR.
For most people, BMR is the single biggest chunk of the calories they burn each day, often around 60 to 70 percent of the total. That is why it is such a useful starting point: once you know roughly how many calories you burn at rest, you can build a realistic picture of how much you burn in a full, active day, and how much to eat for your goal.
If you are brand new to all of this, do not worry. You do not need to memorise any of it. Just enter your details above, and use the rest of this page to understand what your number means.
What your BMR result means
Your result is an estimate of the calories your body needs per day at rest. On its own, your BMR is not the number of calories you should eat, and it is not the total you burn in a normal day, because you also move around, work, and exercise.
Here is the simple way to read it:
- A higher BMR usually reflects a larger body, more muscle, being younger, or being male. None of that is good or bad, it is just biology.
- A lower BMR is common with a smaller frame, less muscle, older age, or being female.
- Your real daily need is higher. To find the calories you actually burn in a day, multiply your BMR by an activity factor. That total is called your TDEE, and you can work it out with our TDEE calculator.
Think of BMR as the foundation and TDEE as the full building.
How the BMR calculation works
This tool uses the Mifflin-St Jeor equation, which research has found to be one of the most accurate BMR formulas for the general population, typically landing within about 10 percent of a person’s true resting metabolism. It uses four inputs: your weight, height, age, and sex.
The Mifflin-St Jeor formula
Working in metric units (kilograms and centimetres):
- Men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5
- Women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161
If you enter imperial units (pounds and feet/inches), the calculator converts them to metric first, so you get the same accurate result either way.
Other formulas you might see
You may come across two older equations. The Harris-Benedict formula is the original, from 1919 and revised in 1984; it tends to slightly overestimate for modern populations. The Katch-McArdle formula is excellent but needs your body-fat percentage, which most beginners do not know. For a simple, reliable starting point without extra measurements, Mifflin-St Jeor is the sensible default, which is why we use it here.
Example calculations
Seeing the formula in action makes it click. Here are two worked examples.
Example 1: a 30-year-old man (metric)
Weight 80 kg, height 180 cm, age 30:
BMR = (10 × 80) + (6.25 × 180) − (5 × 30) + 5 = 800 + 1125 − 150 + 5 = 1,780 calories/day.
Example 2: a 35-year-old woman (imperial, kg and feet)
Weight 150 lb (68 kg), height 5 ft 5 in (165 cm), age 35:
BMR = (10 × 68) + (6.25 × 165) − (5 × 35) − 161 = 680 + 1031 − 175 − 161 = 1,375 calories/day.
Notice how the woman’s BMR is lower even at a similar height. That is mostly down to differences in average muscle mass, not anything you are doing right or wrong.
What affects your BMR
Several things shape your resting metabolism, some you can influence and some you cannot:
- Muscle mass: muscle is more metabolically active than fat, so more muscle nudges your BMR up. This is the main lever you can actually pull, through strength training.
- Body size: larger bodies need more energy to run, so they have higher BMRs.
- Age: BMR tends to drift down gradually with age, partly because we naturally lose muscle over time.
- Sex: men usually have a higher BMR than women of the same size, largely due to more muscle on average.
- Genetics, hormones, and health: your genes and things like thyroid function also play a role, which is one reason any calculator is an estimate rather than an exact measurement.
How to use your BMR: a beginner action plan
Your BMR is a starting point, not a diet plan. Here is how to turn it into something useful, step by step:
- Find your maintenance calories (TDEE). Multiply your BMR by an activity factor, or just use our TDEE calculator. This is roughly how many calories you burn in a normal day.
- Pick a goal. To lose weight gently, eat a little below your TDEE; to gain, eat a little above; to maintain, eat around it. Our calorie calculator does this for you.
- Add movement, not just less food. Building the habit matters most. Start with our guide to working out at home and a simple 15-minute routine.
- Be patient and consistent. Small, steady changes beat dramatic ones. See how to stay consistent.
Common mistakes to avoid
- Eating only your BMR calories. Your BMR is what you burn at rest, so eating at that level while also being active can leave you under-fuelled. Base your intake on your TDEE and goal, not your BMR alone.
- Treating the number as exact. Every formula is an estimate. Use it as a guide and adjust based on real-world results over a few weeks.
- Using an adult formula for children. Mifflin-St Jeor is designed for adults. Children and teens have different needs, so speak to a doctor rather than relying on this tool.
- Chasing a "perfect" BMR. There is no single ideal number. What matters is using yours to make sensible, sustainable choices.
Helpful tips
- Weigh yourself at a consistent time (for example, first thing in the morning) for more reliable inputs.
- Recalculate every few weeks or after a noticeable weight change, since your BMR shifts as your body does.
- Protect and build muscle with regular strength work; it is the most sustainable way to support a healthy metabolism.
- Do not slash calories far below your needs. Very low intakes are hard to sustain and can backfire.
Frequently asked questions
What is a BMR calculator and what does it tell me?
A BMR calculator estimates how many calories your body burns at complete rest to keep vital functions running. It tells you your metabolic baseline, which you can then build on to work out your full daily calorie needs.
How do I calculate my BMR?
The most reliable method is the Mifflin-St Jeor equation, which uses your weight, height, age, and sex. This calculator does the maths for you in either metric (kg and cm) or imperial (pounds and feet) units.
What is the BMR formula for men and women?
For men, BMR = (10 × kg) + (6.25 × cm) − (5 × age) + 5. For women, it is the same but you subtract 161 instead of adding 5. The difference reflects average differences in body composition.
Is the Mifflin-St Jeor equation accurate?
It is considered one of the most accurate BMR formulas for the general population, usually within about 10 percent of a person’s measured resting metabolism, and more accurate than the older Harris-Benedict equation for most people.
What is a normal or good BMR?
There is no single "good" BMR, because it depends on your size, age, sex, and muscle. A larger, younger, or more muscular person will naturally have a higher BMR. Focus on using your own number rather than comparing it to others.
What is the difference between BMR and TDEE?
BMR is what you burn at rest. TDEE (Total Daily Energy Expenditure) is what you burn across a whole day including movement and exercise. TDEE is your BMR multiplied by an activity factor, and it is the number you use for calorie goals.
Should I eat only my BMR calories to lose weight?
Generally no. Eating at your BMR while being active can leave you under-fuelled and is hard to sustain. It is usually better to set a modest calorie deficit below your TDEE. If in doubt, speak to a healthcare professional.
How do I use my BMR for a calorie deficit?
First turn your BMR into your TDEE using an activity factor, then eat a modest amount below that TDEE (many people use a 10 to 20 percent reduction) to lose weight gradually. Our calorie calculator handles this for you.
Does BMR change with age, and can I raise it?
Yes, BMR tends to decline slowly with age, partly due to natural muscle loss. You can support it by staying active and building muscle with regular strength training.
Can I use this BMR calculator for children?
No. The Mifflin-St Jeor formula is designed for adults. Children and teenagers have different energy needs, so please consult a doctor or paediatric professional instead.
References
Mifflin MD, St Jeor ST, et al. "A new predictive equation for resting energy expenditure in healthy individuals." The American Journal of Clinical Nutrition, 1990. General guidance on physical activity is available from the U.S. Centers for Disease Control and Prevention (CDC).
What should I do next?
You have your BMR. Here is where to take it next on your beginner journey.
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