BMR calculator
Four numbers and you get what your body burns lying still for a whole day, with the working shown line by line and all four standard formulas side by side.
Leave this empty if you do not have a measurement you trust. It only unlocks the two lean-mass formulas, Katch-McArdle and Cunningham.
How we got your number
Mifflin-St JeorMifflin-St Jeor equation, published in the American Journal of Clinical Nutrition in 1990 and recommended for healthy adults by the Academy of Nutrition and Dietetics. The same maths the BodyPal app uses.
From resting burn to a real day
| How you live | Multiplier | Calories a day |
|---|
Your BMR multiplied by an activity factor gives your total daily energy expenditure, the number you would actually eat to in order to stay the same weight. Pick the row that matches an honest average week, not your best one.
The four BMR formulas side by side
| Formula | BMR | What it uses |
|---|
The headline number uses Mifflin-St Jeor. Katch-McArdle and Cunningham work from lean body mass instead of total weight, so they need a body fat percentage before they can say anything.
Why your BMR is not what you should eat
Nobody lies still for twenty four hours. The moment you stand up, walk to the kitchen, type, fidget, digest a meal or carry shopping, you are burning above your BMR, and those additions are not small: for a desk worker they add about 20 per cent, and for someone on their feet all day closer to 80 per cent.
Digestion alone takes roughly 10 per cent of what you eat, which is why the lightest activity factor in the table above is 1.2 rather than 1.0. Eating at your BMR is therefore not maintenance and not a gentle deficit; it is a steep one, and it is the most common reason a plan falls apart in week three.
Use the resting figure as a floor and a reference point, then work from your daily total. The daily calorie calculator takes the same inputs and adds a goal, a pace, macros and the date you would reach a target weight.
BMR, RMR and what a lab actually measures
A true basal reading requires you to sleep at the testing site, wake without sitting up, and breathe into a hood after a twelve-hour fast in a temperature-controlled room. Almost nobody does this outside a research setting.
What clinics measure instead is resting metabolic rate: twenty minutes lying quietly, no overnight stay. The looser conditions let a little digestion and muscle tone creep in, so RMR reads about 10 per cent higher than BMR. Both are measured by indirect calorimetry, which tracks the oxygen you consume and the carbon dioxide you produce.
The equations on this page were fitted to measured resting data, so what they print sits between the two definitions. For deciding what to eat, the gap does not matter. For comparing one calculator against another, it explains a fair share of the difference.
The headline figure uses Mifflin-St Jeor (1990), the equation the Academy of Nutrition and Dietetics rates most accurate for healthy adults. The other three formulas are shown for comparison. Nothing you enter is stored or sent anywhere. How we verify our data →
BMR FAQs
What is a normal BMR?
Most adults land between 1,200 and 2,000 calories a day. A 30 year old woman of 70 kg and 170 cm has a BMR of about 1,450; a man of the same size about 1,620. Bigger, younger and more muscular bodies burn more at rest.
Does BMR slow down with age?
A little. BMR falls roughly 1 to 2 percent per decade after your twenties, mostly because muscle is lost. Keeping or building muscle offsets most of that drop, which is why lifting matters more as you get older.
Can you increase your BMR?
Yes, but slowly. Each kilogram of muscle burns about 13 calories a day at rest, so gaining 5 kg of muscle adds roughly 65 calories. Crash diets do the opposite: eating far below BMR for weeks makes the body burn less.
Is BMR the same as RMR?
Almost. BMR is measured after a full night of sleep and 12 hours without food, in a lab. RMR is measured under normal conditions and reads about 10 percent higher. Online calculators estimate BMR, and the difference rarely matters in practice.
Why is my BMR different on other calculators?
Different formulas. Harris-Benedict, from 1919, usually reads 5 to 10 percent higher than Mifflin-St Jeor, and Katch-McArdle changes with the body fat percentage you type in. The table above shows all four for your numbers.
Do I need my body fat percentage?
Only for Katch-McArdle. Mifflin-St Jeor needs weight, height, age and sex, and is accurate enough for most people. If you know your body fat from a scan, enter it and the Katch-McArdle line will be the better estimate.
