What Is BMR? Basal Metabolic Rate Explained

Updated March 2026 · 10 min read

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How BMR Works

Basal Metabolic Rate (BMR) is the number of calories your body requires to perform its most basic life-sustaining functions—breathing, blood circulation, cell production, nutrient processing, and temperature regulation—while at complete rest. It represents the minimum amount of energy your body needs to stay alive if you were to lie in bed all day without moving, eating, or even digesting food.

According to the National Institutes of Health (NIH), BMR accounts for approximately 60–75% of total daily energy expenditure in most adults. This makes it by far the largest component of your daily calorie burn—far exceeding the calories you burn through exercise or digestion. For a person with a BMR of 1,700 calories per day, that means roughly 1,020 to 1,275 of those calories are consumed just keeping your organs functioning.

Understanding your BMR matters because it forms the foundation for any calorie-based diet or nutrition plan. Whether you want to lose fat, gain muscle, or simply maintain your current weight, knowing your BMR lets you calculate your Total Daily Energy Expenditure (TDEE) and set an appropriate calorie target. Nutritionists, dietitians, and fitness professionals all use BMR as the starting point for building personalized meal plans.

The BMR Formulas: Harris-Benedict vs. Mifflin-St Jeor

Two primary equations are used to estimate BMR. Both require your weight, height, age, and sex as inputs, but they were developed decades apart and differ in accuracy.

Harris-Benedict Equation (1919, revised 1984)

Originally published by James Arthur Harris and Francis Gano Benedict in 1919, this was the first widely used BMR prediction formula. It was revised by Roza and Shizgal in 1984 to improve accuracy:

Men: BMR = 88.362 + (13.397 × weight in kg) + (4.799 × height in cm) − (5.677 × age)

Women: BMR = 447.593 + (9.247 × weight in kg) + (3.098 × height in cm) − (4.330 × age)

Mifflin-St Jeor Equation (1990)

Developed by M.D. Mifflin and S.T. St Jeor, this equation is considered the gold standard by the Academy of Nutrition and Dietetics. A 2005 study in the Journal of the American Dietetic Association found it was the most reliable predictor, accurate within 10% for 82% of non-obese individuals.

Men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5

Women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161

Worked Example

A 30-year-old male, 5'10" (178 cm), 180 lbs (82 kg):

Mifflin-St Jeor:

BMR = (10 × 82) + (6.25 × 178) − (5 × 30) + 5

BMR = 820 + 1,112.5 − 150 + 5 = 1,787.5 cal/day

Harris-Benedict (revised):

BMR = 88.362 + (13.397 × 82) + (4.799 × 178) − (5.677 × 30)

BMR = 88.362 + 1,098.6 + 854.2 − 170.3 = 1,870.9 cal/day

Notice that the Harris-Benedict result is about 83 calories higher. This overestimation is consistent with the research, which is why most modern tools (including the BMR calculator) default to the Mifflin-St Jeor equation.

Key Terms You Should Know

Basal Metabolic Rate (BMR) — The number of calories your body burns at complete rest over 24 hours, measured in a post-absorptive state (12 hours after eating) in a thermally neutral environment.
Resting Metabolic Rate (RMR) — Similar to BMR but measured under less strict conditions. RMR is typically 10–20% higher than BMR because it includes slight movement and recent digestion. Many online calculators actually estimate RMR, not true BMR.
Thermic Effect of Food (TEF) — The energy required to digest, absorb, and process nutrients. TEF accounts for roughly 8–15% of total daily energy expenditure. Protein has the highest thermic effect at 20–30%, compared to 5–10% for carbohydrates and 0–3% for fats.
Lean Body Mass (LBM) — Your total body weight minus fat mass. Lean tissue (muscle, bone, organs) is metabolically active and the primary driver of BMR. You can estimate yours with the lean body mass calculator.
Metabolic Adaptation — The reduction in BMR that occurs when you significantly reduce calorie intake or lose weight over time. Research shows BMR can decrease by 15–20% beyond what weight loss alone would predict.

Factors That Affect BMR

Your BMR is not a fixed number. Multiple factors influence how many calories your body burns at rest, and understanding them helps explain why two people of the same weight can have very different metabolic rates.

Factor	Effect on BMR	Magnitude
Muscle Mass	More muscle = higher BMR	~6–7 cal/lb/day vs. ~2 cal/lb for fat
Age	BMR decreases with age	~1–2% decline per decade after 20
Sex	Males typically have higher BMR	~5–10% higher than females of same size
Body Size	Larger bodies burn more at rest	Taller/heavier = proportionally higher BMR
Genetics	Inherited metabolic variation	Up to 200–300 cal/day difference
Thyroid Function	Thyroid hormones regulate metabolism	Hypothyroidism can lower BMR by 15–40%
Climate	Cold exposure increases BMR	~5–20% increase in extreme cold

Average BMR by Age and Sex

The following table shows approximate BMR values based on average body sizes, according to data published by the Food and Agriculture Organization (FAO) and reviewed research. Individual results will vary based on body composition.

Age Range	Average Male BMR (cal/day)	Average Female BMR (cal/day)
18–25	1,800–2,000	1,400–1,550
26–35	1,700–1,900	1,350–1,500
36–45	1,650–1,850	1,300–1,450
46–55	1,550–1,750	1,250–1,400
56–65	1,450–1,650	1,200–1,350
66+	1,350–1,550	1,150–1,300

Practical Examples: Using BMR in Real Life

Here are three scenarios showing how different people can use their BMR to set calorie targets.

Example 1: Weight Loss for a Sedentary Office Worker

Sarah is 35 years old, 5'5" (165 cm), 160 lbs (73 kg), and works a desk job with minimal exercise.

BMR (Mifflin-St Jeor) = (10 × 73) + (6.25 × 165) − (5 × 35) − 161 = 730 + 1,031.25 − 175 − 161 = 1,425 cal/day

TDEE = 1,425 × 1.2 (sedentary) = 1,710 cal/day

For 1 lb/week fat loss: 1,710 − 500 = 1,210 cal/day target

Since 1,210 is close to the commonly recommended floor of 1,200 calories for women, Sarah might aim for a gentler 250-calorie deficit (1,460 cal/day) and add light walking to increase her TDEE instead.

Example 2: Muscle Gain for an Active Lifter

Mike is 28, 6'0" (183 cm), 175 lbs (79 kg), and lifts weights 5 days per week.

BMR = (10 × 79) + (6.25 × 183) − (5 × 28) + 5 = 790 + 1,143.75 − 140 + 5 = 1,799 cal/day

TDEE = 1,799 × 1.725 (very active) = 3,103 cal/day

Lean bulk surplus: 3,103 + 250 = 3,353 cal/day target

Example 3: Maintenance for a Moderately Active Person

Anna is 42, 5'6" (168 cm), 145 lbs (66 kg), and exercises 3 times per week.

BMR = (10 × 66) + (6.25 × 168) − (5 × 42) − 161 = 660 + 1,050 − 210 − 161 = 1,339 cal/day

TDEE = 1,339 × 1.55 (moderately active) = 2,075 cal/day to maintain

Tips to Support a Healthy Metabolism

Build and maintain muscle mass. Resistance training 2–4 times per week is the single most effective way to raise your BMR. A study in Medicine & Science in Sports & Exercise found that 10 weeks of resistance training increased resting metabolic rate by an average of 7%.
Eat enough protein. Aim for 0.7–1.0 g of protein per pound of body weight. Protein has the highest thermic effect of any macronutrient (20–30%), meaning your body burns more calories digesting it. Use the protein calculator to find your target.
Avoid extreme calorie restriction. Eating below your BMR for extended periods triggers metabolic adaptation, reducing your BMR by up to 15–20%. A moderate deficit of 500 calories below TDEE is more sustainable.
Get adequate sleep. Research published in the Annals of Internal Medicine shows that sleep deprivation (less than 6 hours) can reduce BMR by 5–20% and increase hunger hormones.
Stay hydrated. Drinking 500 ml (17 oz) of water can temporarily boost metabolic rate by 24–30% for 60–90 minutes, according to a study in the Journal of Clinical Endocrinology & Metabolism.
Manage stress levels. Chronic stress elevates cortisol, which can promote fat storage and reduce lean muscle mass over time, indirectly lowering BMR.

BMR vs. RMR: Which Should You Use?

BMR and RMR (Resting Metabolic Rate) are often used interchangeably, but they are measured under different conditions. True BMR requires 8 hours of sleep, 12 hours of fasting, and a controlled lab environment. RMR is measured under less strict conditions and is typically 10–20% higher than BMR.

For practical purposes, the difference rarely matters. Most online calculators, including the formulas above, estimate something closer to RMR. When paired with an activity multiplier to calculate TDEE, the activity factors are calibrated to work with these estimates. Use whichever number you have, and adjust your calorie target based on real-world results after 2–4 weeks.

Find Your BMR Now

Get your personalized Basal Metabolic Rate using both the Harris-Benedict and Mifflin-St Jeor equations.

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Disclaimer: This guide is for informational purposes only and does not constitute medical or nutritional advice. Always consult a qualified healthcare professional for decisions specific to your situation.

Frequently Asked Questions

What is a good BMR for my age?

A typical BMR for a 30-year-old male weighing 180 lbs (82 kg) at 5'10" (178 cm) is approximately 1,775 calories per day using the Mifflin-St Jeor equation. For a 30-year-old female at 140 lbs (64 kg) and 5'5" (165 cm), BMR is roughly 1,380 calories per day. BMR naturally declines by about 1–2% per decade after age 20, according to research published in the American Journal of Clinical Nutrition. There is no single "good" BMR because it depends on your body composition, height, weight, and genetics. A higher BMR relative to your body size typically indicates more lean muscle mass.

How is BMR different from TDEE?

BMR measures calories burned at complete rest, while TDEE (Total Daily Energy Expenditure) includes all daily activity. BMR typically accounts for 60–75% of your TDEE, according to the National Institutes of Health. The remaining 25–40% comes from physical activity (exercise and non-exercise movement) and the thermic effect of food. To calculate TDEE, you multiply your BMR by an activity factor ranging from 1.2 (sedentary) to 1.9 (extremely active). You can use the TDEE calculator to find your full daily calorie expenditure.

Can I increase my BMR?

Yes, the most effective way to increase your BMR is by building lean muscle mass through resistance training. Each pound of muscle burns approximately 6–7 calories per day at rest, compared to about 2 calories per pound of fat, according to research from the National Strength and Conditioning Association. Over time, adding 10 pounds of muscle can raise your resting metabolism by 40–70 calories daily. Other factors that temporarily boost BMR include eating adequate protein (which has a high thermic effect of 20–30%), staying well-hydrated, getting 7–9 hours of sleep, and avoiding prolonged calorie restriction.

Which BMR formula is most accurate?

The Mifflin-St Jeor equation is considered the most accurate BMR formula for the general population. A 2005 study in the Journal of the American Dietetic Association compared multiple prediction equations and found it predicted BMR within 10% of measured values in 82% of non-obese individuals and 70% of obese individuals. The Harris-Benedict equation, developed in 1919, tends to overestimate BMR by about 5%. For individuals who know their body fat percentage, the Katch-McArdle formula may provide even better accuracy since it factors in lean body mass directly.

How many calories does my body burn at rest?

Most adults burn between 1,200 and 2,000 calories per day at complete rest, which is their BMR. For example, an average 35-year-old woman (5'4", 150 lbs) burns roughly 1,400 calories at rest, while an average 35-year-old man (5'10", 185 lbs) burns about 1,800 calories. These calories fuel essential functions including breathing, blood circulation, cell production, and brain activity. Your brain alone consumes approximately 20% of your resting energy, according to the Proceedings of the National Academy of Sciences. Use the BMR calculator to get a personalized estimate.

Does BMR change with age?

Yes, BMR decreases with age at a rate of approximately 1–2% per decade after age 20. A study published in Public Health Nutrition found that BMR declines by roughly 150 calories per decade in men and 100 calories per decade in women. This decline is primarily driven by the loss of lean muscle mass (sarcopenia), which accelerates after age 30 at a rate of 3–8% per decade. Hormonal changes, including declining levels of growth hormone and testosterone, also contribute. However, regular resistance training and adequate protein intake (0.7–1.0 g per pound of body weight) can significantly slow this decline.