BMR Calculator
Last Updated:
Find the calories your body burns at rest, plus your TDEE and kilojoules a day. Works for women and men, in kilograms or pounds.
Quick answer: BMR is the calories your body burns at complete rest. Using Mifflin-St Jeor: Male BMR = 10×weight(kg) + 6.25×height(cm) − 5×age + 5; Female uses −161 instead of +5. Multiply by an activity factor (1.2–1.9) to get your TDEE.
Basal Metabolic Rate (BMR)
—
Calories burned at complete rest
Based on the Mifflin-St Jeor equation. It is an estimate, not a measurement.
📐 Formula
Male BMR = (10 × weight kg) + (6.25 × height cm) − (5 × age) + 5. Female: same but −161 instead of +5. TDEE = BMR × Activity Factor
How to Use the BMR Calculator
Enter your age, sex, height and weight
Pick kilograms and centimeters or pounds and inches, then enter your age, sex, height and weight. These are the only four variables in the Mifflin-St Jeor formula. Use your current weight, not a goal weight.
Select your activity level
Choose the activity multiplier that best reflects your typical week: sedentary (desk job, little exercise), lightly active (exercise 1–3 days), moderately active (exercise 3–5 days), very active (hard exercise 6–7 days) or extremely active (physical job plus exercise).
Read your BMR and TDEE
BMR is your calorie baseline at rest and TDEE is your estimated daily calorie burn. The calculator shows both in calories and kilojoules. Use TDEE for any diet or weight management planning.
Adjust for your goal
Subtract 500 calories from TDEE for about 1 lb (0.5 kg) of weight loss a week, or add 250–500 calories for muscle gain.
BMR vs TDEE: The Critical Difference
Your Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest — just to maintain heart function, breathing, temperature regulation, and cellular repair. It is the largest part of daily calorie burn for most people. TDEE (Total Daily Energy Expenditure) adds activity on top: exercise, walking, non-exercise activity thermogenesis (NEAT: fidgeting, standing, gesturing), and the thermic effect of food (the energy your body uses to digest what you eat).
For weight management, TDEE is the number that matters. Eating at TDEE maintains weight. Eating below it creates a deficit; above it, a surplus. BMR alone significantly underestimates calorie needs and should never be used as a weight-loss calorie target. Recovery matters too — inadequate sleep is linked to a less favorable metabolic and hormonal profile even at the same calorie intake; our bedtime and wake-up time calculator can help you plan a schedule that supports it.
Why this calculator uses the Mifflin-St Jeor formula
The Mifflin-St Jeor equation was published in 1990 from measurements of 498 healthy adults aged 19 to 78 (Mifflin et al., American Journal of Clinical Nutrition). A 2005 systematic review published in the Journal of the American Dietetic Association (Frankenfield et al.) compared the four equations most used in practice (Harris-Benedict, Mifflin-St Jeor, Owen and WHO/FAO/UNU). It found Mifflin-St Jeor predicted resting metabolic rate within 10% of the measured value for more people than any other equation, with the narrowest error range. The same review also found noteworthy errors for some individuals, so treat your result as an estimate. The formula: Male BMR = (10 × kg) + (6.25 × cm) − (5 × age) + 5. Female: same but −161 instead of +5. Example: a 35-year-old woman, 65 kg, 168 cm: (10×65) + (6.25×168) − (5×35) − 161 = 650 + 1,050 − 175 − 161 = 1,364 calories/day BMR. Multiply by an activity factor (1.375 for lightly active) = 1,876 TDEE.
Why BMR Changes Over Time
BMR tends to fall with age, mainly because muscle mass gradually declines. Resistance training helps you keep muscle, and muscle is more active than fat at rest. Elia's estimates put skeletal muscle at about 13 calories per kilogram a day and fat tissue at about 4.5, roughly 6 and 2 calories per pound. Wang et al. (2010) found those values hold across adulthood, running about 3% lower after age 50.
Activity Multipliers: Honest Self-Assessment Matters
Choosing an activity level turns this into a BMR calculator with exercise: your BMR is multiplied by that level to give the calories you burn in a day. Most people overestimate their activity level, which leads to overeating relative to actual needs. "Lightly active" means 1–3 days of genuine exercise per week, not occasional walks. "Moderately active" requires consistent 3–5 days of exercise at moderate intensity. If you have an office job and exercise 3 times per week for 45 minutes, lightly active (1.375) is likely more accurate than moderately active (1.55). The difference between these two multipliers on a 1,500 BMR is 263 calories a day, which at about 7,700 calories per kilogram adds up to about 12.5 kg a year if the mistake is repeated every day.
How to use your BMR to lose weight
Your BMR is the floor, not the target. To plan weight loss, start from TDEE and subtract a moderate deficit. The calculator shows that figure as the calories for about 1 lb (0.5 kg) of loss a week.
Take the 35-year-old woman (65 kg, 168 cm) from the Mifflin-St Jeor example above. Her BMR is 1,364 calories and her TDEE is 1,876. Subtracting 500 gives 1,376 calories, only 12 above her BMR. A smaller deficit of 250 calories a day (1,626) is the gentler choice, and the calorie calculator shows both options side by side.
| Option | Calories a day | Above her BMR |
|---|---|---|
| Maintain (TDEE) | 1,876 | 512 |
| Subtract 250 | 1,626 | 262 |
| Subtract 500 | 1,376 | 12 |
If your target lands near or below your BMR, slow the pace rather than cutting further, and read the FAQ below on eating under your BMR.
How to Calculate BMR by Hand: Worked Example
Using the Mifflin-St Jeor equation, the formula this calculator uses, for a 35-year-old male, 80 kg, 178 cm tall:
Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5.
10×80 + 6.25×178 − 5×35 + 5 = 800 + 1,112.5 − 175 + 5 = 1,742.5 calories/day.
Women use the same structure with a different constant: BMR = 10×weight + 6.25×height − 5×age − 161. For a 35-year-old woman at the same weight and height: 800 + 1,112.5 − 175 − 161 = 1,576.5 calories/day, which is 166 fewer calories than the male result, a gap built into the formula's sex term, which reflects average differences in body composition at the same weight and height.
Why does BMR represent only the "resting" baseline, not total daily needs?
BMR measures the energy required for basic involuntary functions alone — breathing, circulation, cell repair — assuming complete physical rest, and explicitly excludes digestion, movement, and exercise. It is intentionally the floor of the calculation, not the answer to "how many calories should I eat," which is what a full TDEE (Total Daily Energy Expenditure) figure (BMR multiplied by an activity factor) is for.
Why is Mifflin-St Jeor used instead of older equations?
Mifflin-St Jeor was built from 498 healthy adults in 1990, and in that study the 1919 Harris-Benedict equations overestimated resting energy expenditure by 5%. A 2005 dietetics review later favored Mifflin-St Jeor, so this calculator uses it alone.
How does it compare to the older Harris-Benedict equation?
Harris-Benedict dates from 1919. In the 1990 Mifflin-St Jeor study, the 1919 equations overestimated measured resting energy expenditure by 5% (p less than 0.01). The 2005 review above is why it is the default here. Older equations still turn up in legacy calculators and older textbooks.
How much does BMR actually decline with age?
The formula's −5×age term shows the mechanism directly: BMR declines by roughly 5 calories per year of age at a constant weight and height, primarily reflecting the gradual loss of metabolically active muscle mass over time. A 55-year-old with identical weight and height to the 35-year-old example above has a BMR about 100 calories/day lower — a modest but real effect that resistance training can partly offset by preserving muscle mass.
Why does honest activity-level self-assessment matter more than most people expect?
Multiplying BMR by an inflated activity factor (choosing "very active" when actual activity is moderate) is one of the most common reasons calculated calorie targets fail to produce expected results — a single activity-level tier can shift the total TDEE estimate by 200–400 calories/day, larger than many people's intended weekly deficit.
Frequently Asked Questions
BMR (Basal Metabolic Rate) is the calories your body burns at complete rest just to keep basic functions running. TDEE (Total Daily Energy Expenditure) is your BMR multiplied by an activity factor — it's how many calories you actually burn per day.
It is an estimate. The 2005 dietetics review that favored it still found noteworthy errors for some individuals, and older adults and US-residing ethnic minorities were underrepresented in the studies. Compare your result with how your weight actually changes over a few weeks and adjust.
Male BMR = 4.536 × weight (lb) + 15.875 × height (in) − 5 × age + 5. Female BMR uses −161 instead of +5. The two multipliers come from converting the metric formula: 10 × 0.4536 kg per pound and 6.25 × 2.54 cm per inch. The calculator does the conversion for you.
Not in this equation, which uses age, sex, height and weight only. The 1990 Mifflin-St Jeor study found fat-free mass was the best single predictor of resting energy expenditure, so equations built on lean body mass need a body fat percentage. You can estimate yours with the body fat calculator.
The Mifflin-St Jeor equation was built from healthy adults aged 19 to 78, so its results for children and teens are untested. This calculator accepts ages 15 to 100. For anyone under 18, ask a pediatrician or dietitian about energy needs instead of relying on this estimate.
Multiply calories by 4.184, because one calorie (kcal) equals 4.184 kJ. A BMR of 1,700 calories is about 7,113 kJ a day. The calculator shows both.
Eating 500 calories below your TDEE creates a 3,500 calorie weekly deficit, which a common rule of thumb equates to about 1 pound of fat loss per week. Commonly cited general guidance is not to go below about 1,200 calories a day (women) or 1,500 calories a day (men); that is not medical advice, so check with a doctor or dietitian first.
Eating at your BMR is already a deficit for most people, because the activity multipliers above put TDEE 20% to 90% higher than BMR. Going below it for long periods is generally not advised, because it can risk muscle loss and nutrient deficiencies. Check with a doctor or dietitian before eating much less than your BMR.
Yes. The Mifflin-St Jeor formula subtracts 161 for women and adds 5 for men, a 166 calorie gap at the same age, weight and height. The 1990 study derived that sex term from measurements of 247 women and 251 men.
Sources & Methodology
The formula and the claims about it come from these peer-reviewed sources (abstracts read on November 3, 2026):
- Mifflin MD et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr, 1990
- Frankenfield D et al. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. J Am Diet Assoc, 2005
- Wang Z et al. Specific metabolic rates of major organs and tissues across adulthood. Am J Clin Nutr, 2010