BMR calculator
Your BMR is the energy your body uses just to keep you alive at rest — breathing, circulation, keeping warm. We use the Mifflin-St Jeor equation, the most accurate of the common formulas. Multiply it by your activity to get the calories you actually burn in a day.
Used only for the equation constants.
Daily calories
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Protein a day
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BMR
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Maintenance (TDEE)
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We won't show a target that low.
Your goal maths lands below a level we consider safe to recommend, so we're showing the floor instead. Very low intakes are hard to sustain and can do more harm than good. If losing weight matters to you, a smaller deficit you can actually keep beats a large one you can't. If food or eating feels distressing, please talk to someone — there are support links in the footer.
Why these numbers?
Calories use the Mifflin-St Jeor equation for BMR, which a 2005 review of four common equations found the most reliable, though any equation can be off for one person. It is multiplied by a common activity factor (not an official standard) for maintenance (TDEE). Fat loss shows maintenance minus 20%, which is our rule; guidelines more often suggest a deficit of 500 to 750 calories a day. Building muscle adds 10%, also our rule.
Protein: losing fat or building muscle assumes you exercise, so it shows 1.4–2.0 g per kg of body weight, the range sports-nutrition research gives for most people who exercise. "Maintain" shows 0.8 g per kg, the recommended minimum for adults. From 65, it shows at least 1.0–1.2 g per kg (1.2 or more if you are active), the range set out for older adults. The big number is the middle of the range.
These are population estimates, not a prescription. Your real needs vary. See our editorial policy for how we source this.
See also the TDEE calculator and the fasting calculator.
What BMR means
BMR, or basal metabolic rate, is the number of calories your body would burn in a day spent lying at rest. For an adult with an ordinary routine, it makes up half or more of the calories burned in a day. The calculator predicts it from four numbers, because measuring it takes laboratory equipment.
How the BMR calculator works
Enter your units, sex at birth, age, weight and height. Your BMR appears in the results panel once all four are filled in. Next to it you get your maintenance calories, a daily target and a protein range. Those extra figures come from multiplying BMR by your activity level, which the TDEE calculator explains in full.
The BMR itself comes from the Mifflin-St Jeor equation, published in 1990. In words:
- Multiply your weight in kg by 10.
- Multiply your height in cm by 6.25 and add it.
- Multiply your age in years by 5 and take it away.
- Add 5 if you are a man, or take away 161 if you are a woman.
Pounds, stone, feet and inches are converted to kg and cm before the sum runs. A 2005 review compared Mifflin-St Jeor with three other common equations against measured values. It came within 10% of the measured figure for more people than the other three did. Even so, the result for one person can still be well off.
A worked example
Take a man aged 40, 180 cm (5 ft 11 in) tall, weighing 85 kg (187 lb).
- Weight: 85 × 10 = 850.
- Height: 180 × 6.25 = 1,125.
- Age: 40 × 5 = 200, taken away.
- Sex: add 5.
His BMR is 850 + 1,125 − 200 + 5 = 1,780 kcal a day. If he loses 10 kg, the weight part falls to 750 and his BMR to 1,680 kcal. Ten more birthdays would take off another 50 kcal.
BMR vs TDEE
BMR is the floor of your energy use, measured lying still. TDEE, your total daily energy expenditure, adds everything you do on top, such as walking, working and exercise. TDEE is the number that decides whether you lose, keep or gain weight.
The gap between the two is large for everyone. Adults living ordinary lives cannot keep their long-term energy use much below 1.4 times BMR. For the man above, that means at least about 2,490 kcal a day. Use the TDEE calculator to choose an activity level and see your own figure.
BMR and intermittent fasting
Your fasting schedule changes when you eat, while your BMR depends on your body size and age. The figure only moves when your weight does, by about 10 kcal for each kilogram.
Whether fasting itself slows metabolism has little research behind it. In one small 22-day study, 16 adults fasted every other day and their resting metabolic rate did not change measurably. That counts as early evidence, from a small, short study.
If you are pregnant, under 18 or underweight, don’t use a BMR figure to plan a diet without a doctor.
Related tools and guides
The fasting calculator shows your eating window for 16:8, 18:6 or another schedule. The body fat calculator shows how much of your weight is lean mass. For what fasting does and doesn’t change in the body, and how strong each finding is, read our evidence-graded benefits guide.
Frequently asked
What is a normal BMR?
No single figure is normal, because BMR depends on your weight, height, age and sex. On the Mifflin-St Jeor equation, a woman of 35 who is 165 cm and 70 kg comes out at about 1,395 kcal a day. A man of 40 who is 180 cm and 85 kg comes out at about 1,780 kcal.
Should I eat my BMR to lose weight?
Your BMR covers only the energy you use lying still. Adults living ordinary lives burn at least about 1.4 times their BMR over the long run, so eating at BMR is already a large cut. The calculator's fat-loss figure starts from your maintenance calories instead, and never drops below 1,200 kcal (women) or 1,500 kcal (men).
Does BMR go down when you lose weight?
Yes, on the equation. Every kilogram you lose takes 10 kcal off the Mifflin-St Jeor result, so losing 10 kg lowers it by about 100 kcal a day. Re-enter your weight every few kilograms to keep your figures current.
Does intermittent fasting slow your metabolism?
The evidence is early. In a 22-day study of 16 adults who were not obese, fasting every other day did not measurably change resting metabolic rate. Over that time they lost about 2.5% of their body weight. Longer and larger trials are needed before anyone can say more.
Why does the BMR calculator ask for my sex at birth?
The equation ends with a different constant for each sex. It adds 5 for men and takes off 161 for women, so the same body measurements give a man a BMR 166 kcal higher. Sex at birth is used for nothing else.