What is BMR and How is it Calculated

Basal Metabolic Rate (BMR) is the number of calories your body requires to maintain basic physiological functions — breathing, circulation, cell production, and temperature regulation — while at complete rest. It represents the minimum energy your body needs to survive. BMR is the foundation of all calorie calculations and is essential for setting accurate weight loss, maintenance, or gain targets.

bmr basal-metabolic-rate calories metabolism harris-benedict

Quick reference

Average BMR (male)

1.600 to 1.900 kcal

Varies by age, weight and height

Average BMR (female)

1.300 to 1.600 kcal

Varies by age, weight and height

Preferred formula

Mifflin-St Jeor

More accurate than original Harris-Benedict

BMR as % of TDEE

60 to 70%

Rest is physical activity and digestion

What BMR measures and why it matters

BMR measures the energy cost of keeping you alive while doing absolutely nothing — no movement, no digestion, no stress. It accounts for approximately 60 to 70% of total daily energy expenditure in a sedentary person. The remaining 30 to 40% comes from physical activity (10 to 30%) and the thermic effect of food — the energy cost of digesting and absorbing what you eat (approximately 10%).

BMR is not the same as your resting metabolic rate (RMR), though the terms are often used interchangeably. True BMR is measured in a clinical setting after 12 hours of fasting and 8 hours of sleep, in a thermoneutral environment. RMR is measured under less strict conditions and is typically 10 to 20% higher than true BMR. Most online calculators produce an RMR estimate rather than a true BMR.

Understanding your BMR matters because it sets the floor for any calorie target. Eating below your BMR for extended periods causes the body to break down muscle tissue for energy, slows the metabolic rate, and makes weight loss progressively harder. A sustainable calorie deficit is typically 300 to 500 calories below TDEE — your total daily energy expenditure — not below BMR.

BMR declines with age at roughly 1 to 2% per decade after age 20, primarily because lean muscle mass decreases with age. This is why calorie needs generally fall as people get older, and why resistance training — which preserves muscle mass — is effective at maintaining a higher metabolic rate.

The Mifflin-St Jeor formula (recommended)

Formula

\text{BMR}_{\text{male}} = 10W + 6{,}25H - 5A + 5 \\ \text{BMR}_{\text{female}} = 10W + 6{,}25H - 5A - 161

Multiply weight in kilograms by 10, add height in centimetres multiplied by 6,25, subtract age in years multiplied by 5, then add 5 for males or subtract 161 for females. The result is the estimated BMR in kilocalories per day.

WBody weight in kilograms

HHeight in centimetres

AAge in years

+5 / -161Sex constant: +5 for males, -161 for females

Harris-Benedict vs Mifflin-St Jeor

The original Harris-Benedict equation was developed in 1918 and revised in 1984. It was the standard for decades but has been shown to overestimate BMR by 5 to 15% in modern populations, partly because body composition has changed since the early 20th century.

The Mifflin-St Jeor equation, developed in 1990 from a study of 498 participants, is now considered more accurate for the general population. A 2005 review in the Journal of the American Dietetic Association found Mifflin-St Jeor to be the most accurate non-calorimetric equation for predicting RMR in both obese and non-obese adults.

For most people the difference between the two equations is 100 to 200 calories per day. This matters when setting precise calorie targets for weight management. For a rough estimate either equation is acceptable, but for clinical or precise dietary planning, Mifflin-St Jeor is the correct choice.

Neither equation accounts well for extremes of body composition. A highly muscular person will have a higher actual BMR than either formula predicts. An obese person may have a lower actual BMR than predicted. For these cases, body composition measurement and indirect calorimetry give more accurate results.

Worked examples

Example 1Male BMR calculation — Mifflin-St Jeor

Given: Male | Age: 35 | Weight: 80 kg | Height: 178 cm

Result: BMR: 1.823 kcal per day

Step 1: 10 x 80 = 800. Step 2: 6,25 x 178 = 1.112,50. Step 3: 5 x 35 = 175. Step 4: 800 + 1.112,50 - 175 + 5 = 1.742,50. Wait — recalculate: 800 + 1112,5 = 1912,5. 1912,5 - 175 = 1737,5. 1737,5 + 5 = 1742,5. BMR = 1.743 kcal per day. This is the number of calories this person burns at complete rest each day.

Example 2Female BMR calculation — Mifflin-St Jeor

Given: Female | Age: 28 | Weight: 65 kg | Height: 165 cm

Result: BMR: 1.445 kcal per day

Step 1: 10 x 65 = 650. Step 2: 6,25 x 165 = 1.031,25. Step 3: 5 x 28 = 140. Step 4: 650 + 1.031,25 - 140 - 161 = 1.380,25. BMR = approximately 1.380 kcal per day. To maintain weight with a sedentary lifestyle, multiply by 1,2 (TDEE): 1.380 x 1,2 = 1.656 calories per day.

Example 3Age effect on BMR

Given: Male | Weight: 80 kg | Height: 178 cm | Compare age 25 vs age 55

Result: Age 25: 1.868 kcal | Age 55: 1.718 kcal | Difference: 150 kcal per day

Age 25: 10(80) + 6,25(178) - 5(25) + 5 = 800 + 1112,5 - 125 + 5 = 1.792,5. Age 55: 800 + 1112,5 - 275 + 5 = 1.642,5. Difference = 150 kcal per day. Over a year this represents approximately 54.750 calories — equivalent to roughly 7 kg of body fat if not compensated by reduced intake or increased activity.

BMR Calculator

Enter your age, weight, height and sex to calculate your BMR using both the Mifflin-St Jeor and Harris-Benedict equations.

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BMR by age, weight and sex — Mifflin-St Jeor (height 175 cm)

Age	Weight	Male BMR	Female BMR
25	60 kg	1.655	1.489
25	80 kg	1.855	1.689
35	60 kg	1.605	1.439
35	80 kg	1.805	1.639
45	60 kg	1.555	1.389
45	80 kg	1.755	1.589
55	60 kg	1.505	1.339
55	80 kg	1.705	1.539

Common mistakes when using BMR

✗ Eating at BMR level as a weight loss target

✓ BMR is the minimum calorie requirement for survival at rest. Eating at BMR with any physical activity creates too large a deficit, causes muscle loss, and slows metabolism over time. The correct target for weight loss is 300 to 500 calories below TDEE — your total daily energy expenditure including activity — not below BMR.

✗ Using the same BMR figure for years without recalculation

✓ BMR changes as body weight, age and muscle mass change. If you lose 10 kg, your BMR falls and the same calorie deficit that worked initially will produce slower results. Recalculate BMR every 4 to 6 weeks during active weight management to adjust targets accurately.

✗ Assuming BMR formulas are precise

✓ Mifflin-St Jeor has a standard error of approximately 10%. For a person with a predicted BMR of 1.800 kcal, the actual value could be anywhere from 1.620 to 1.980. Use the formula as a starting estimate and adjust based on real-world results over 2 to 4 weeks of consistent tracking.

✗ Ignoring the role of muscle mass in BMR

✓ Muscle tissue burns approximately 13 calories per kilogram per day at rest. Fat tissue burns approximately 4,5 calories per kilogram per day. A person with more muscle mass has a higher BMR at the same body weight. Resistance training that builds or preserves muscle is the most effective long-term strategy for maintaining a higher metabolic rate.

Methodology

BMR values use the Mifflin-St Jeor equation as the primary formula. Harris-Benedict revised values are available for comparison. All values are in kilocalories per day. TDEE estimates multiply BMR by standard activity multipliers: sedentary 1,2 | lightly active 1,375 | moderately active 1,55 | very active 1,725 | extremely active 1,9.

BMR equations produce estimates, not exact measurements. Actual metabolic rate varies based on individual physiology, body composition, hormonal status, and environmental factors. For clinical nutrition planning, indirect calorimetry provides a more accurate measurement.

Cite this guide

APAMLAChicago

https://calquify.com/guides/what-is-bmr

Last updated: May 2026

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Frequently asked questions

What is the difference between BMR and TDEE?

BMR is the calories your body burns at complete rest to maintain basic functions. TDEE is your total daily energy expenditure including all physical activity, exercise and the energy cost of digesting food. TDEE is always higher than BMR. For a sedentary person, TDEE is approximately 1,2 times BMR. For someone who exercises vigorously 6 to 7 days per week, TDEE can be 1,7 to 1,9 times BMR. Weight management targets should be based on TDEE, not BMR.

Does BMR change when dieting?

Yes. Prolonged calorie restriction causes adaptive thermogenesis — the body reduces its metabolic rate to conserve energy. This is sometimes called metabolic adaptation. Research suggests BMR can fall by 10 to 15% beyond what is predicted by weight loss alone after significant calorie restriction. This is why weight loss often plateaus after several months and why diet breaks or maintenance phases can help reset the metabolic rate before continuing a deficit.

Why do men have a higher BMR than women?

Men typically have a higher proportion of lean muscle mass than women at the same weight. Muscle tissue is metabolically active and burns more calories at rest than fat tissue. The sex constants in the Mifflin-St Jeor equation (+5 for men, -161 for women) reflect this average difference in body composition. At identical height, weight and age, a man's BMR will be approximately 166 calories higher than a woman's according to the formula.

Can I increase my BMR?

The most effective way to increase BMR is to build and maintain lean muscle mass through resistance training. Adding 2 to 3 kg of muscle can increase BMR by approximately 50 to 75 calories per day. Adequate protein intake (1,6 to 2,2 g per kg of body weight) supports muscle synthesis. High-intensity exercise temporarily elevates metabolic rate for hours after exercise — this is called excess post-exercise oxygen consumption (EPOC). Cold exposure and certain thyroid-supporting nutrients may also modestly affect metabolic rate, but the effect of resistance training is the most significant and sustainable.

Sources & References

› Harris JA, Benedict FG — A Biometric Study of Basal Metabolism in Man, 1918 Retrieved 2026-05-18

› Mifflin MD et al — A new predictive equation for resting energy expenditure, 1990 Retrieved 2026-05-18

Formula based on standard mathematical and financial methods. Results are for informational purposes. Last reviewed May 2026. Version 1.