BMR calculator: basal metabolic rate at rest
BMR, or basal metabolic rate, is how many calories your body burns in a day at complete rest. The Mifflin-St Jeor equation (1990): 10 × weight in kg + 6.25 × height in cm − 5 × age, plus 5 for men or minus 161 for women. A 30-year-old woman, 165 cm, 65 kg, comes out at about 1,370 kcal. Your burn with movement is in the TDEE calculator, how much to eat in the calorie calculator.
Track it every day in Telegram
Where the number comes from
The formula, a worked example and where it stops working
What BMR is
BMR, your basal metabolic rate, is how many calories your body burns in a day at complete rest: breathing, circulation, body temperature, brain and organs. The calculator uses the Mifflin-St Jeor equation (Mifflin MD, St Jeor ST et al., American Journal of Clinical Nutrition, 1990): 10 × weight in kg + 6.25 × height in cm − 5 × age, plus 5 for men or minus 161 for women. Example: a 30-year-old woman at 165 cm and 65 kg gets 650 + 1,031 − 150 − 161, about 1,370 kcal.
That isn't how much to eat, it's what you'd burn lying in bed all day. For a daily target that counts your movement, use the calorie calculator.
By the calculator's own maths, BMR is anywhere from 53% (activity ×1.9) to 83% (sedentary, ×1.2) of your total daily burn. Most of the calories you use in a day go on simply staying alive, not on moving.
What affects your BMR
The equation has four inputs, and each pulls its own weight. That is why two people on the same scale reading can be hundreds of calories apart.
- Weight — every kilogram adds 10 kcal a day (10 × weight)
- Height — every 10 cm adds 62.5 kcal (6.25 × height)
- Age — every year takes 5 kcal away, so a decade costs 50 (5 × age)
- Sex — a man with the same numbers gets 166 kcal more: +5 versus −161
- Body composition, thyroid hormones and illness change metabolism too, but the formula cannot see them — it only knows these four numbers
BMR chart for women by age and weight
Find your age and weight; where they meet is your BMR in kcal a day. The chart assumes 165 cm: if you are taller, add about 6 kcal per centimetre (6.25 × height), if shorter, take it off.
You can see the formula at work: one 10 kg step to the right is +100 kcal, one 10-year step down is −50.
| Age | 50 kg | 60 kg | 70 kg | 80 kg | 90 kg | 100 kg |
|---|---|---|---|---|---|---|
| 20 years | 1,270 | 1,370 | 1,470 | 1,570 | 1,670 | 1,770 |
| 30 years | 1,220 | 1,320 | 1,420 | 1,520 | 1,620 | 1,720 |
| 40 years | 1,170 | 1,270 | 1,370 | 1,470 | 1,570 | 1,670 |
| 50 years | 1,120 | 1,220 | 1,320 | 1,420 | 1,520 | 1,620 |
| 60 years | 1,070 | 1,170 | 1,270 | 1,370 | 1,470 | 1,570 |
| 70 years | 1,020 | 1,120 | 1,220 | 1,320 | 1,420 | 1,520 |
Calories a day at complete rest. Woman, 165 cm. Mifflin-St Jeor, the same maths as in the BMR calculator.
BMR chart for men by age and weight
The same chart for a man of 178 cm. At equal weight and age, the gap to the women's chart is the sex offset plus the height difference.
| Age | 60 kg | 70 kg | 80 kg | 90 kg | 100 kg | 110 kg |
|---|---|---|---|---|---|---|
| 20 years | 1,618 | 1,718 | 1,818 | 1,918 | 2,018 | 2,118 |
| 30 years | 1,568 | 1,668 | 1,768 | 1,868 | 1,968 | 2,068 |
| 40 years | 1,518 | 1,618 | 1,718 | 1,818 | 1,918 | 2,018 |
| 50 years | 1,468 | 1,568 | 1,668 | 1,768 | 1,868 | 1,968 |
| 60 years | 1,418 | 1,518 | 1,618 | 1,718 | 1,818 | 1,918 |
| 70 years | 1,368 | 1,468 | 1,568 | 1,668 | 1,768 | 1,868 |
Calories a day at complete rest. Man, 178 cm. Mifflin-St Jeor, the same maths as in the BMR calculator.
A worked example with real numbers
Take a woman of 30: 65 kg, 165 cm, training twice a week. Here it is step by step — exactly what the calculator above does.
- 10 × 65 kg = 650
- 6.25 × 165 cm = 1,031
- 5 × 30 years = 150 — subtract that
- the female offset of −161 — subtract that too
- 650 + 1,031 − 150 − 161 = 1,370 kcal a day. That is her BMR, the same number the calculator shows
- training twice a week means an activity factor of 1.375, so her full daily burn comes to 1,884 kcal — the number the calculator shows next to it as TDEE
BMR formulas: Mifflin-St Jeor, Harris-Benedict and lean-mass equations
There is more than one BMR formula. The oldest still in use is the Harris-Benedict equation from 1918, and plenty of calculators online run it or its revised version, which is why their numbers sometimes differ from ours. Mifflin-St Jeor was derived in 1990 from 498 healthy adults aged 19-78, men and women, normal weight and obese, with energy expenditure measured by indirect calorimetry.
A review that compared the four most widely used equations, these two included — Frankenfield D et al., Journal of the American Dietetic Association, 2005 — found Mifflin-St Jeor landed within 10% of lab-measured expenditure more often than the rest, with the narrowest spread of error. The same authors say plainly that for an individual the miss can still be sizeable, and that older adults were thinly represented in the studies.
Some equations work from lean mass, your weight minus fat; the best known is Katch-McArdle. They suit people carrying a lot of muscle, but they need a body-fat percentage. You can estimate yours from tape measurements in the body fat calculator.
In plain terms: the calculator says 1,370, and this woman's real burn is most likely somewhere between 1,230 and 1,510 kcal: plus or minus 10%, as in the Frankenfield review, 2005. Treat the number as a starting point, not a verdict.
BMR vs RMR: what the formula really estimates
Strictly speaking, basal metabolic rate is measured under tight conditions: first thing in the morning, fasted, lying down, in a warm room. Burn at rest without all that is called RMR, resting metabolic rate.
The Mifflin-St Jeor paper is titled "A new predictive equation for resting energy expenditure", so the formula actually predicts resting burn, and calling it BMR is a habit this calculator shares with most others. For food planning the difference does not matter: the next step multiplies it by an activity factor anyway.
What to do with the number next
BMR on its own is not a food target. The next step is to multiply it by an activity factor to get your total daily burn — that is what the TDEE calculator for maintenance calories does, with a chart for all five activity levels.
If you want to lose weight, a deficit comes off that burn, and BMR becomes the floor: the food target does not go below it. How to pick a pace that keeps you above it is what the calorie deficit calculator shows.
The formula does not fit during pregnancy and breastfeeding, under 18, with thyroid disease or with a lot of muscle. The full list, and how to check your number against the scale over two weeks, is in the calorie calculator.
How we calculate
The formulas and limits are the same as in the CalCash bot: the site and the bot run the same code. Here is what goes into the number.
- Resting burn (BMR) — the Mifflin-St Jeor equation: 10 × weight in kg + 6.25 × height in cm − 5 × age, plus 5 for men or minus 161 for women (Mifflin MD, St Jeor ST et al., American Journal of Clinical Nutrition, 1990).
- That is your burn at complete rest: breathing, heartbeat, brain, body temperature. The TDEE calculator adds all the moving you do on top with an activity factor.
Your BMR is only the floor. What you actually eat in a day is the part worth tracking, and that is the job of a bot that counts calories from a photo or a voice note — it adds up your day and holds it against your target.
Frequently asked questions
What is BMR in simple terms?
It is how many calories your body burns in a day if you lie still and do nothing: breathing, heartbeat, brain and body temperature. By the Mifflin-St Jeor equation, for a 30-year-old woman, 165 cm and 65 kg, that is about 1,370 kcal; for a 30-year-old man, 178 cm and 80 kg, about 1,770. What you burn with movement on top is a different number, TDEE.
Which BMR formula is the most accurate?
Of the four most widely used equations, a 2005 review found Mifflin-St Jeor the most reliable: it landed within 10% of lab-measured burn more often than the others. That is the one this calculator uses. The older Harris-Benedict equation usually gives slightly different numbers. The only way to know your own metabolism exactly is a lab measurement.
Can I just eat my BMR?
Better not. BMR is your burn at complete rest, and you move during the day, so a weight-loss target is worked out from TDEE, not BMR. Our deficit calculator and the bot take 250-750 kcal off TDEE depending on pace, but no more than 20%, and advise not going below BMR.
Does BMR drop with age?
In the formula, yes: every year takes off 5 kcal, so 50 kcal a decade at the same weight and height. In real life, losing muscle you do not use usually adds to that, and the formula cannot see it. That is why strength training is the usual advice: it helps you keep muscle.
Why is my BMR lower than my friend's at the same weight?
Because weight is not the only thing the formula reads. Every 10 cm of height adds about 60 kcal, every 10 years of age takes 50 away. Then there is body composition: at the same number on the scale, the person carrying more muscle burns more — and that part the formula cannot see at all.
Do I recalculate BMR after losing weight?
Yes. Weight sits right inside the equation, so 5 kg down is roughly 50 kcal off your basal rate. Recalculate whenever your weight moves by 3-4 kg, otherwise you are aiming at an old number.
Reminders
Water and weight