Basal Metabolic Rate Formulas and Typical Values | How Many kcal by Age and Sex, and Your Daily Calorie Burn
Every diet book and app mentions basal metabolism, yet there are several formulas, and many people are confused when each app gives a different number. This guide uses concrete figures to compare a BMR formula developed for Japanese people with the main international formulas, shows how much BMR changes with age and weight, and explains how to estimate your total daily calorie burn using physical activity levels.
What basal metabolism is: the energy you use even when doing nothing
Basal metabolism (basal metabolic rate, BMR) is the amount of energy used to keep you alive, beating your heart, breathing and maintaining body temperature, while you lie awake and at rest. Even if you did not move at all for a whole day, you would still burn roughly this many calories.
BMR makes up a large share of daily calorie burn: about 60% for a “moderately active” lifestyle. The rest is physical activity such as commuting, housework and exercise, plus the energy used to digest and absorb food. Because BMR is the foundation for estimating daily calorie burn, it is the first thing you calculate when planning a diet.
The main BMR formulas
Measuring BMR directly requires special equipment, so in practice it is estimated from sex, age, height and weight. Four representative formulas are shown below.
| Formula | Calculation | Characteristics |
|---|---|---|
| National Institute of Health and Nutrition (Japan) equation | (0.0481 × weight kg + 0.0234 × height cm − 0.0138 × age − constant) × 1000 ÷ 4.186, with the constant 0.4235 for men and 0.9708 for women | Built from measurements of Japanese people; considered to have a small error for Japanese adults |
| Reference BMR value × weight | Multiply a “BMR per kg of body weight” for your sex and age group by your weight | The method used in Japan's Dietary Reference Intakes from the Ministry of Health, Labour and Welfare; for ages 18 and over |
| Harris-Benedict equation (revised) | Men 88.362 + 13.397 × weight + 4.799 × height − 5.677 × age; women 447.593 + 9.247 × weight + 3.098 × height − 4.33 × age | A classic formula based on measurements of Western subjects; tends to run high for Japanese people |
| Mifflin-St Jeor equation | 10 × weight + 6.25 × height − 5 × age, then +5 for men or −161 for women | Widely used in apps outside Japan |
The reference BMR values (kcal per kg per day) are, for men, 23.7 at 18 to 29, 22.5 at 30 to 49, 21.8 at 50 to 64, 21.6 at 65 to 74 and 21.5 at 75 and over; for women, 22.1 at 18 to 29, 21.9 at 30 to 49 and 20.7 at 50 and over (Dietary Reference Intakes for Japanese, 2020 edition).
The same person can differ by more than 100 kcal depending on the formula
Here is the BMR of the same people calculated with all four formulas (in kcal, rounded to the nearest whole number).
| Person | NIHN (Japan) | Reference × weight | Harris-Benedict | Mifflin |
|---|---|---|---|---|
| Woman, 20, 158 cm, 50 kg | 1,160 | 1,105 | 1,313 | 1,227 |
| Woman, 30, 160 cm, 55 kg | 1,196 | 1,205 | 1,322 | 1,239 |
| Woman, 50, 156 cm, 55 kg | 1,107 | 1,139 | 1,223 | 1,114 |
| Man, 25, 172 cm, 65 kg | 1,525 | 1,541 | 1,643 | 1,605 |
| Man, 40, 170 cm, 70 kg | 1,522 | 1,575 | 1,615 | 1,568 |
| Man, 60, 168 cm, 68 kg | 1,422 | 1,482 | 1,465 | 1,435 |
The Harris-Benedict equation comes out about 130 to 150 kcal higher than the Japanese NIHN equation, especially for young women. When apps disagree about your BMR, the formula is usually the reason. A 100 kcal daily difference adds up to 3,000 kcal a month, or about 0.4 kg of body fat, so it is worth knowing which formula your figure comes from when you plan a diet. For Japanese people, the NIHN equation is the recommended starting point.
How much age and weight change BMR
In the NIHN equation, with everything else equal, BMR changes by about 3.3 kcal for each year of age, about 11.5 kcal for each kilogram of weight and about 5.6 kcal for each centimetre of height.
| Age | Woman (160 cm, 55 kg) | Man (170 cm, 65 kg) |
|---|---|---|
| 20 | 1,229 kcal | 1,530 kcal |
| 30 | 1,196 kcal | 1,497 kcal |
| 40 | 1,163 kcal | 1,464 kcal |
| 50 | 1,130 kcal | 1,431 kcal |
| 60 | 1,097 kcal | 1,398 kcal |
| 70 | 1,064 kcal | 1,365 kcal |
Even with the same build, a 20-year-old and a 50-year-old differ by about 100 kcal a day. That is one reason people feel they are gaining weight on the same diet they ate when they were younger. BMR also falls as you lose weight: a 30-year-old woman at 160 cm burns 1,196 kcal at 55 kg but 1,138 kcal at 50 kg. This change is part of why weight loss slows down partway through a diet.
Daily calorie burn = BMR × physical activity level
The calories you actually burn in a day (estimated energy requirement) are found by multiplying BMR by a physical activity level (PAL). Japan's Dietary Reference Intakes set three levels.
| Physical activity level | Typical lifestyle | Ages 18 to 64 | Ages 65 to 74 |
|---|---|---|---|
| Low (I) | Most of the day spent sitting; no exercise habit | 1.50 | 1.45 |
| Moderate (II) | Mainly desk work, but active through commuting, housework or light exercise | 1.75 | 1.70 |
| High (III) | A standing or mobile job, or a habit of vigorous exercise | 2.00 | 1.95 |
For a 30-year-old woman, 160 cm and 55 kg (BMR 1,196 kcal), daily calorie burn is 1,793 kcal at low, 2,092 kcal at moderate and 2,391 kcal at high. For a 40-year-old man, 170 cm and 70 kg (1,522 kcal), it is 2,282 kcal at low, 2,663 kcal at moderate and 3,043 kcal at high. The same person can differ by about 600 kcal depending on activity, so choosing the level that fits your life matters. If unsure, choose moderate and adjust while watching how your weight changes.
To maintain your weight, you eat about the same as this calorie burn. How many kcal a day to eat when you want to lose weight is explained in how many kilograms you can lose in a month.
Calculating your own BMR
- 1
Enter your height and weight
Enter them in the height and weight fields of the BMI and ideal weight calculator. The values carry over when you switch tabs.
- 2
Choose sex, age and activity level
On the “BMR and calories” tab, enter your sex and age, and choose a physical activity level of low, moderate or high.
- 3
Check your BMR and calorie burn
It shows your BMR, daily calorie burn and a guide to the intake that keeps your weight steady. A table also shows calorie burn for each activity level and compares the results of the four formulas.
For a guide to body size itself, see BMI formula and obesity categories, and for a target weight, see the standard and beauty weight by height chart.
FAQ
- What is the formula for basal metabolic rate?
- For Japanese people the National Institute of Health and Nutrition equation is recommended. For men it is (0.0481 × weight kg + 0.0234 × height cm − 0.0138 × age − 0.4235) × 1000 ÷ 4.186; for women, replace the final constant with 0.9708. A 30-year-old woman, 160 cm and 55 kg, comes out at about 1,196 kcal, and a 40-year-old man, 170 cm and 70 kg, at about 1,522 kcal.
- Why do apps show different BMR figures?
- Because they use different formulas. The Harris-Benedict equation, built from Western data, can come out 130 to 150 kcal higher than the Japanese NIHN equation for young Japanese women. Body composition scales also use body fat percentage and other measures in their estimates, so they can give yet another value.
- How do I calculate my daily calorie burn?
- Multiply BMR by your physical activity level. For ages 18 to 64 the levels are low 1.50, moderate 1.75 and high 2.00. Someone with a BMR of 1,196 kcal and a moderate lifestyle burns 1,196 × 1.75 = about 2,092 kcal.
- How much does BMR fall with age?
- In the NIHN equation, with the same build, it falls by about 3.3 kcal per year, or about 33 kcal per decade. A woman of 160 cm and 55 kg burns 1,229 kcal at 20 and 1,130 kcal at 50, a difference of about 100 kcal over 30 years.
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