The number of calories a human burns just by existing varies quite a bit from person to person. Factors like age, sex, weight, height, muscle mass, metabolism, and activity level all impact one’s basal metabolic rate (BMR). BMR is the minimum number of calories needed to fuel your body’s basic functions like breathing, heartbeat, brain function, hormone production, etc. It’s the amount of energy your body would burn if you did absolutely nothing all day – just laid in bed. Understanding your basal metabolic rate can help with weight loss efforts, reaching fitness goals, and maintaining a healthy lifestyle. This article will explore the average BMR ranges, methods for calculating your BMR, and the estimated total calories burned per day by simply existing.
What is Basal Metabolic Rate?
Your basal metabolic rate is the minimum number of calories your organs need to function each day. It’s the calories required to keep your body at rest. Also referred to as your metabolism, BMR accounts for 60-75% of the calories you burn each day. The other 25-40% comes from physical activity and digesting food. BMR is measured when you are fully at rest – meaning you are not eating, sleeping, or doing any physical activity. The main factors that determine your BMR are:
- Age – BMR slows as you get older
- Sex – Men tend to have a higher BMR than women
- Weight – Heavier people burn more calories at rest
- Height – Taller people tend to have a higher BMR
- Body Composition – Muscle burns more calories than fat
- Genetics and Hormones – These impact your metabolism
So a 20 year old male who is 6’0″ tall, weighs 180 lbs with 15% body fat would have a much higher BMR than a 40 year old female who is 5’2″, weighs 150 lbs with 30% body fat.
Average BMR Ranges
According to the United States Department of Health, the average Basal Metabolic Rate values for adults are:
For men:
- 1,600 to 1,800 calories per day for sedentary men
- 1,800 to 2,000 for moderately active men
- 2,000-2,200 for very active men
For women:
- 1,300 to 1,500 calories per day for sedentary women
- 1,500 to 1,700 calories for moderately active women
- 1,700 to 1,900 calories for very active women
As illustrated, men tend to burn more calories per day at rest than women. This is primarily due to men naturally having less body fat and more muscle mass than women. The more active someone is also increases their basal metabolic rate. So if two women are the same age and weight, but one exercises often and has more muscle mass, she will burn more calories per day at rest.
Calculating Your BMR
There are several equations that allow you to calculate your basal metabolic rate based on your individual stats like age, weight and body composition. Here are some of the most common BMR formulas:
Mifflin St Jeor Equation:
For men: BMR = 10 x weight (kg) + 6.25 x height (cm) – 5 x age (years) + 5
For women: BMR = 10 x weight (kg) + 6.25 x height (cm) – 5 x age (years) – 161
Harris Benedict Formula:
For men: BMR = 88.362 + (13.397 x weight in kg) + (4.799 x height in cm) – (5.677 x age in years)
For women: BMR = 447.593 + (9.247 x weight in kg) + (3.098 x height in cm) – (4.330 x age in years)
Katch McArdle Formula:
BMR = 370 + (21.6 x lean body mass in kg)
*Lean body mass = total body weight – body fat weight
You can calculate your BMR online by plugging your stats into a basal metabolic rate calculator. This will give you a starting point estimation, but for the most accuracy you can get your BMR professionally tested. This involves breathing into a machine that analyzes your oxygen consumption at rest.
Here is an example of how to calculate BMR for a 25 year old woman who is 5’5″ (165 cm), weighs 145 lbs (65.8 kg) with 25% body fat percentage:
Mifflin St Jeor Formula:
BMR = 10 x 65.8 kg + 6.25 x 165 cm – 5 x 25 years – 161
BMR = 1,387 calories/day
Harris Benedict Formula:
BMR = 447.593 + (9.247 x 65.8 kg) + (3.098 x 165 cm) – (4.330 x 25 years)
BMR = 1,398 calories/day
Katch McArdle Formula:
Lean Body Mass = Total Weight – (Total Weight x Body Fat %)
= 145 lbs – (145 lbs x 25%)
= 145 lbs – 36.25 lbs
= 108.75 lbs
Lean Body Mass in kg = 108.75 lbs / 2.20462 lbs per kg
= 49.3 kg
BMR = 370 + (21.6 x 49.3 kg)
= 1,400 calories/day
All three formulas provide very similar results for this woman’s basal metabolic rate. She would need to consume around 1,400 calories per day if she was completely at rest to maintain normal organ function.
Daily Calorie Burn
Your BMR is the calories burned by just laying in bed all day, but we obviously burn more calories than that going about our daily lives. The average person burns 15-30% more calories on top of their BMR each day. This number varies based on activity level.
Here is an estimate of the total calories burned per day including BMR plus additional energy expenditure:
Sedentary (little to no exercise):
BMR X 1.2 = Total calorie burn
For example, if BMR is 1,400 calories:
1,400 X 1.2 = 1,680 calories burned per day
Moderately Active (light exercise 3-5 days/week):
BMR X 1.375 = Total calorie burn
For BMR of 1,400 calories:
1,400 X 1.375 = 1,925 calories burned per day
Very Active (intense exercise 6-7 days/week):
BMR X 1.55 = Total calorie burn
For BMR of 1,400 calories:
1,400 X 1.55 = 2,170 calories burned per day
Factors That Impact Calorie Burn
Many variables affect the number of calories your body needs and burns each day. Let’s explore some of the key factors:
Age
As you age, your metabolism slows down. Studies show that by age 60, your BMR can decrease by 2-3% per decade. This is due to loss of muscle mass as you get older. Less muscle means your body requires less energy (calories) for basic functioning.
Sex
Males tend to have less body fat and more muscle than females. This means men generally have a 5-10% higher basal metabolic rate than women of the same age and weight. Testosterone and other male sex hormones contribute to men burning more calories at rest.
Body Size & Composition
People who carry more weight, especially more muscle, burn more calories than people who weigh less. Fat is not metabolically active like muscle, but it still takes energy to sustain body fat. This means overweight people tend to have a higher BMR than skinny people. Building lean muscle through exercise is one of the best ways to increase your metabolism.
Diet
What you eat impacts calories burned. Protein requires the most energy to digest – 20-35% of protein calories are burned during digestion. Comparatively, only 5-15% of fat calories and 5-10% of carbohydrate calories are burned through digestion. High protein diets tend to slightly boost your metabolism.
Genetics
Some people inherit a naturally faster metabolism. Your genes determine your cells’ efficiency at converting calories to energy. People can have a 5-10% difference in BMR simply due to genetic factors. Ethnicity can also impact your resting metabolism.
External Temperature
When it’s cold outside, your body burns more calories to maintain body temperature. This is called adaptive thermogenesis. The opposite occurs in hot climates, where your metabolism may slightly decrease to prevent overheating.
Frequent Eating
Eating more frequently can slightly increase your metabolism, especially if you consume protein. This is due to the Thermic Effect of Food (TEF) – or the energy required to digest meals. Small, protein-rich meals rev up your metabolism.
Medical Conditions & Medications
Thyroid disorders, diabetes, hormonal imbalances, steroid use, and other medical conditions or medications can impact metabolic rate. Both overactive and underactive thyroids strongly influence BMR and daily calorie needs.
Ways to Boost Your Metabolism
While some factors like age and genetics are beyond your control, there are steps you can take to counteract a slowing metabolism. Strategies to increase calorie burn include:
Exercise, Especially Strength Training
Adding regular cardio and strength training workouts is one of the most effective ways to boost your metabolism. Muscle is very metabolically active, so the more lean muscle you build, the more calories your body burns day and night.
Eat More Protein
Protein has a higher Thermic Effect of Food than carbs or fats. It also helps maintain and build calorie-burning muscle. Getting 25-35% of your daily calories from protein sources like meat, eggs, dairy and legumes can increase your metabolism.
Stay Hydrated
Drinking adequate water helps your body efficiently metabolize stored fat and eliminates waste products that can slow metabolism. Men should drink 15-17 cups of fluid per day, women 11-13 cups.
Get Enough Sleep
Lack of sleep disrupts hormones that regulate hunger and metabolism. Most adults need 7-9 hours of sleep per night. Going to bed early and avoiding screen time before bed helps ensure restful sleep.
Manage Stress
Chronic stress and elevated cortisol levels promote fat storage and weight gain. Make time for relaxing activities like yoga, meditation, massage and warm baths to keep stress in check.
Consume Metabolism-Boosting Foods
Certain foods contain compounds and capsaicin that may slightly boost metabolism. Options include green tea, coffee, chili peppers, apple cider vinegar, turmeric, ginger, high-fiber foods, oatmeal, berries, nuts and leafy greens.
The Takeaway
Your basal metabolic rate dictates the minimum number of calories needed to sustain your body’s basic functions if you were completely inactive. BMR typically accounts for 60-75% of your total daily calorie expenditure. The number of calories your body burns day-to-day varies widely based on your age, sex, size, body composition, and activity level. Things like your diet, muscle mass, and genetics also impact metabolic rate. While some factors are unavoidable, regular exercise, a high protein diet, and other lifestyle habits can help counteract a slowing metabolism.
