How to Calculate BMR
Your basal metabolic rate (BMR) is the number of calories your body burns at complete rest — lying still, doing nothing, just staying alive. It is the foundation of every calorie plan: once you know your BMR, you multiply it by your activity level to get your daily calorie needs. The BMR calculator above works it out in seconds, but this page shows you the formula and the maths so you can calculate it by hand and understand what the number means.
BMR is not a guess. It comes from equations built on measurements of thousands of people, and the best of them — Mifflin-St Jeor — is accurate to within about 10 percent for most adults. Below you will find the formula for men and women, two worked examples, a comparison of the three main formulas, and the mistakes that make hand calculations wrong.
The BMR Formula (Mifflin-St Jeor)
The Mifflin-St Jeor equation is the formula most dietitians and clinicians use today, because it has proven the most accurate in modern studies. There are two versions, one for men and one for women, and they differ only in the final number.
Men: BMR = 10 × weight in kg + 6.25 × height in cm − 5 × age in years + 5
Women: BMR = 10 × weight in kg + 6.25 × height in cm − 5 × age in years − 161
The difference between the two formulas is 166 calories. That gap reflects average body composition: at the same weight, height and age, men typically carry more muscle, and muscle burns more energy at rest than fat does.
What Each Part Means
Weight contributes 10 calories per kilogram — the biggest single term for most people. Height contributes 6.25 calories per centimetre. Age subtracts 5 calories per year, reflecting the slow loss of muscle and metabolic rate as we get older. The final constant (+5 for men, −161 for women) adjusts for the average sex difference in body composition. Nothing else enters the formula: it does not ask about your activity, your diet or your fitness, because BMR is by definition the burn at complete rest.
Worked Example: A 30-Year-Old Man
Take a man aged 30, weighing 70 kg, 175 cm tall. Work through the formula term by term:
- Weight term: 10 × 70 = 700
- Height term: 6.25 × 175 = 1,093.75
- Age term: 5 × 30 = 150, subtracted
- Constant: + 5
- Total: 700 + 1,093.75 − 150 + 5 = 1,648.75, rounded to 1,649 calories a day
That is the default result the BMR calculator above shows when it loads — 1,649 kcal a day, or about 69 calories an hour at complete rest. It is also the BMR the calorie and TDEE tools on this site start from.
Worked Example: A 25-Year-Old Woman
Now a woman aged 25, weighing 60 kg, 165 cm tall:
- Weight term: 10 × 60 = 600
- Height term: 6.25 × 165 = 1,031.25
- Age term: 5 × 25 = 125, subtracted
- Constant: − 161
- Total: 600 + 1,031.25 − 125 − 161 = 1,345.25, rounded to 1,345 calories a day
Her BMR is 304 calories lower than the man’s, even though she is only 10 kg lighter and 10 cm shorter. Most of the gap comes from the 166-calorie sex difference and her lower weight. If you want to check your own figure, enter your numbers in the calculator above and compare them with a hand calculation — they should match exactly.
BMR for Different People
The table below shows BMR for a range of adults, all calculated with Mifflin-St Jeor, so you can find the row closest to you.
| Person | Calculation | BMR |
|---|---|---|
| Man, 25, 75 kg, 178 cm | 750 + 1,112.5 − 125 + 5 | 1,743 kcal |
| Man, 40, 80 kg, 178 cm | 800 + 1,112.5 − 200 + 5 | 1,718 kcal |
| Man, 55, 80 kg, 178 cm | 800 + 1,112.5 − 275 + 5 | 1,643 kcal |
| Woman, 25, 60 kg, 165 cm | 600 + 1,031.25 − 125 − 161 | 1,345 kcal |
| Woman, 40, 65 kg, 165 cm | 650 + 1,031.25 − 200 − 161 | 1,320 kcal |
| Woman, 55, 65 kg, 165 cm | 650 + 1,031.25 − 275 − 161 | 1,245 kcal |
Look at the pattern. Between age 25 and 55, BMR falls by about 100 calories a day at the same weight — the 5-calories-a-year age term at work. And weight dominates everything: the 80 kg men burn roughly 300 calories a day more at rest than the 60 kg woman, simply because there is more body to maintain.
The Three BMR Formulas Compared
Mifflin-St Jeor is not the only formula. The calculator above offers three, and each has its place. The table shows what each one gives for the same man — 30 years old, 70 kg, 175 cm.
| Formula | BMR (man, 30, 70 kg, 175 cm) | Best for |
|---|---|---|
| Mifflin-St Jeor (1990) | 1,649 kcal | Most adults — the recommended default |
| Revised Harris-Benedict (1984) | 1,696 kcal | Comparison with older studies |
| Katch-McArdle (needs body fat %) | 1,580 kcal at 20% body fat | Lean or muscular people |
Harris-Benedict is the oldest formula, from 1919 and revised in 1984. It usually gives a slightly higher number than Mifflin-St Jeor — 47 calories higher for our example man. Katch-McArdle is different: it uses lean body mass instead of total weight, so it needs your body fat percentage. At 20% body fat, our 70 kg man has 56 kg of lean mass and a BMR of 370 + 21.6 × 56 = 1,580 calories. For very muscular or very lean people, Katch-McArdle is the most accurate of the three, because it counts the tissue that actually burns the calories. You can get your body fat percentage from the body fat calculator.
From BMR to Daily Calories
BMR is only the resting part. To get your daily calorie needs, multiply it by an activity factor. The same man with a BMR of 1,649 needs 1,979 calories a day if he is sedentary (× 1.2), 2,556 if moderately active (× 1.55), and 3,133 if extra active (× 1.9). That is why BMR alone never tells you how much to eat — it is the starting point, not the answer. Use the TDEE calculator to do the multiplication, or the calorie calculator to turn it into a daily target with macros.
What Raises and Lowers Your BMR
- More muscle raises it. Muscle burns roughly 13 calories per kg a day at rest, against about 4.5 for fat. Adding 5 kg of muscle adds around 40 to 65 calories a day of resting burn.
- More weight raises it. Every extra kilogram adds 10 calories a day to the formula, whether it is muscle or fat.
- Age lowers it. About 5 calories a year, mostly from muscle loss. Strength training twice a week slows this considerably.
- Crash dieting lowers it. Very low calorie intake triggers adaptive thermogenesis — your body burns less to protect itself. The drop can be 10 to 15 percent on extreme diets.
- Illness and fever raise it. Each degree of fever raises BMR by roughly 7 to 13 percent.
- Cold exposure raises it slightly. Shivering and brown-fat activation burn extra energy, but the effect is small and short-lived.
Common Mistakes When Calculating BMR
- Using pounds instead of kilograms. The formula needs kilograms. Divide pounds by 2.205 first — 154 lb is 70 kg, not 154.
- Using inches instead of centimetres. Height must be in centimetres. Multiply inches by 2.54 — 69 inches is 175 cm.
- Using the wrong constant. Men add 5; women subtract 161. Swapping them shifts the answer by 166 calories.
- Forgetting the age term. It is small per year but adds up: 150 calories at age 30, 275 at age 55.
- Treating BMR as daily needs. BMR is rest only. Eating your BMR while living a normal active life is a built-in deficit of 400 to 1,000 calories.
Related tools: turn your BMR into daily needs with the TDEE calculator, get a full daily target with macros from the calorie calculator, and check your weight category with the BMI calculator. The National Heart, Lung, and Blood Institute explains how BMR fits into healthy weight management.
Summary
Keep the reference figures below handy while you plan.
| Age | Man, 80 kg, 178 cm | Woman, 65 kg, 165 cm |
|---|---|---|
| 25 | 1,793 kcal | 1,395 kcal |
| 35 | 1,743 kcal | 1,345 kcal |
| 45 | 1,693 kcal | 1,295 kcal |
| 55 | 1,643 kcal | 1,245 kcal |
| 65 | 1,593 kcal | 1,195 kcal |
What to remember
- BMR is the calories you burn at complete rest — 60 to 70 percent of your daily total.
- Men burn about 166 calories a day more than women at the same size, through higher muscle mass.
- BMR falls about 5 calories a year, mostly through muscle loss.
- Mifflin-St Jeor is the most accurate formula for most adults; Katch-McArdle is best for very lean or muscular people.
- Multiply BMR by an activity factor (1.2 to 1.9) to get your daily calorie needs.
Your checklist
- Enter your sex, age, weight and height in the calculator above.
- Read your BMR and compare the three formulas.
- Multiply by your activity level to get your daily needs.
- Set your goal target: minus 500 for weight loss, plus 500 for gain.
- Recalculate whenever your weight changes by 5 kg or more.
Mistakes to avoid
- Using pounds instead of kilograms — divide pounds by 2.205 first.
- Using the wrong constant: men add 5, women subtract 161.
- Treating BMR as daily needs — eating only your BMR is a large deficit.
- Forgetting the age term, which adds up to 150 calories between age 25 and 55.
- Crash dieting, which can suppress BMR by 10 to 15 percent.
Frequently Asked Questions
How do I calculate my BMR by hand?
Use the Mifflin-St Jeor equation. For men: 10 × weight in kg + 6.25 × height in cm − 5 × age + 5. For women: the same, but subtract 161 at the end instead of adding 5. A 30-year-old man at 70 kg and 175 cm gets 700 + 1,093.75 − 150 + 5 = 1,649 calories a day.
What is a normal BMR?
For most adults, BMR falls between 1,200 and 2,000 calories a day. Women typically sit between 1,200 and 1,600, men between 1,500 and 2,000. Larger and younger people are at the top of those ranges; smaller and older people at the bottom.
Which BMR formula is most accurate?
Mifflin-St Jeor is the most accurate for most adults, within about 10 percent. Katch-McArdle is better for very lean or muscular people because it uses lean body mass, but it needs your body fat percentage. Harris-Benedict is older and usually reads slightly high.
Does BMR include exercise?
No. BMR is the energy burned at complete rest. Exercise, walking, working and digesting food are all on top. Multiply BMR by an activity factor — 1.2 if sedentary, 1.55 if moderately active — to get your total daily burn.
Can I raise my BMR?
Yes, modestly. Building muscle is the main lever: each kilogram of muscle adds roughly 13 calories a day of resting burn. Eating enough protein and doing strength training twice a week both help. Crash diets do the opposite and lower BMR.
Why is my BMR lower than my friend’s?
Mostly weight, muscle and sex. A heavier person burns more at rest, a muscular person burns more per kilogram, and men burn about 166 calories a day more than women at the same size. Age matters too — BMR falls about 5 calories a year.
Disclaimer: This calculator provides estimates for general information only and is not medical advice. BMR equations are averages and can be off by 10 percent or more for individuals. Consult a doctor or registered dietitian before using BMR to plan a diet, especially if you have a medical condition.