What does losing weight, burning fat, gaining weight, and building muscle have in common? They are all largely dependent on your calorie intake. The food you eat provides your body with energy, which is measured in calories.
A calorie or kilocalorie is the amount of heat needed to raise the temperature of one kilogram of water by one degree Celsius.
You may also have heard of a unit of measure called joules, which is a metric measure used in Europe. There are 4.2 joules to a calorie. However, calories are easier to understand, so that’s the unit we’ll be mainly be using in this article.
Whatever your fitness goal, your diet needs to provide the right amount of energy to achieve it. For example, if you want to lose weight and burn fat, you must consume fewer calories. But, to build muscle and gain weight, you need to eat more.
But, how do you determine the right number of calories for your goal?
Use our accurate BMR calculator to discover the answer!
What is BMR?
BMR stands for Basal Metabolic Rate. Don’t let the unusual word basal confuse you; it’s just another way of saying basic or base.
Your BMR is the amount of energy your body uses per day at rest, at a comfortable temperature, and with an inactive digestive system. We measure that energy in joules or, more commonly, calories.
BMR does not include any calories used during exercise or other types of physical activity, nor the energy used when you eat and digest food. As such, BMR is your energy expenditure while resting and in a fasted state, typically 12 hours after eating (1).
Instead, it’s the energy used for basic (there’s that word again!) metabolic functions, like breathing, pumping blood around your body, brain function, etc. For example, imagine you are quietly sitting in a chair, not eating or moving.
How is BMR Calculated?
Our BMR calculator uses three different equations to determine your Basal Metabolic Rate (2).
The three BMR equations are:
Mifflin St. Jeor Equation
- Men: 10 x weight (kg) + 6.25 x height (cm) – 5 x age (y) + 5
- Women: 10 x weight (kg) + 6.25 x height (cm) – 5 x age (y) – 161
Revised Harris-Benedict Equation
- Men: (13.397m + 4.799h – 5.677a) + 88.362
- Women: (9.247m + 3.098h – 4.330a) + 447.593
(m is mass in kg, h is height in cm, a is age in years)
- BMR = 370 + (21.6 * LBM)
(LBM = Lean Body Mass)
Thankfully, you don’t need to do any of these equations by hand – although you can if you wish! Instead, just select the option you want to use in the settings tab of the calculator.
How To Use The BMR Calculator
Our BMR calculator is straightforward to use. Just follow these step-by-step instructions:
- Select the units – either imperial (pounds and inches) or metric (kilograms and centimeters).
- Enter your weight
- Enter your height
- Enter your age
- Enter your body fat percentage if known (optional)
- Hit “calculate”
Your result will be displayed in calories or joules, depending on the units selected.
What Do the Results Mean?
Your BMR is the number of calories or joules expended while at rest and while your digestive system is inactive, i.e., in a fasted state. In addition to your BMR, you’ll also see displayed your daily calorie needs based on your current activity levels.
Factors that affect these results include:
- Muscle mass – the more muscular you are, the more calories your body uses at rest. Gaining muscle is one of the best ways to increase your BMR.
- Age – BMR tends to decline with age, often because of decreases in muscle mass. Lost muscle is one of the factors that leads to middle age weight gain.
- Genetics – some people have a higher BMR than others and are said to have a “fast metabolism.”
- Weather – cold weather tends to increase BMR as your body will have to use more energy to maintain its core temperature. Being very hot also burns more calories, as your body needs to expend energy to try and keep you cool.
- Pregnancy – being pregnant causes an increase in BMR as more energy is required by the growing fetus. Menopause also affects BMR and can cause it to increase or decrease depending on hormonal changes.
- Supplements and drugs – stimulants can cause BMR to increase, including caffeine. Other medications can cause the BMR to fall, such as some sedatives.
Once you know your BMR, you can use it to calculate the number of calories you need to consume per day to achieve your weight or body composition goal.
The good (no GREAT!) news is that we’ve done that for you, and you can see how many calories you need to consume based on not only your BMR but your current activity levels.
Fasted vs. Non-Fasted BMR
Your BMR is your energy expenditure at rest and in a fasted state. In lab tests, fasted means you won’t have eaten for 8-12 hours.
Why does this matter?
While the food you eat contains calories, eating and digesting food also uses energy. This is called the Thermic (or thermal) Effect of Food, or TEF for short.
Different foods have differing TEFs, so it’s not really practical to include your TEF when trying to calculate your daily energy needs. However, it’s well-known that protein has the highest TEF and causes a significant increase in calorie expenditure. In contrast, fat has the lowest TEF.
This helps explain why high protein diets can be helpful for fat loss – eating more protein increases your metabolic rate (3). However, it’s impossible to say how significant this effect is, as there are too many variables to consider, like portion size, type of protein, and what was also consumed, all of which affect TEF.
How to Use BMR
Armed with your BMR, you can use it to estimate your TDEE, which is short for Total Daily Energy Expenditure.
Remember, BMR is the amount of energy you use at rest during 24 hours. However, most people move around to perform activities of daily living. They may also exercise, all of which increase your calorie expenditure, which we call your TDEE.
The amount of energy used during physical movement is called the Thermal Effect of Activity, or TEA for short. This includes both planned and unplanned physical activity, i.e. structured exercise and day-to-day tasks like walking, mowing the lawn, etc.
That means your TDEE = BMR + TEA
To estimate your TEA and calculate your TDEE from your BMR, you simply multiply your BMR by the appropriate activity factor, as shown below:
- Sedentary = BMR x 1.2 (little or no exercise, desk job)
- Lightly active = BMR x 1.375 (light exercise or sports 1-3 days per week)
- Moderately active = BMR x 1.55 (moderate exercise or sports 6-7 days per week)
- Very active = BMR x 1.725 (hard exercise every day, or exercising twice a day)
- Extra active = BMR x 1.9 (hard exercise two or more times per day, or training for a marathon, triathlon, etc.
For example: Your BMR is 1339 calories per day, and your activity level is moderately active (work out 3-4 times per week).
Your activity factor is 1.55, so your TDEE is 1.55 x 1339 = 2075 calories per day.
This is the total calories you should eat every day if you want to maintain your current weight at your current activity level.
You can calculate these values yourself or, if you take a look at the box just below your BMR result, you’ll see we’ve done the math for you.
To lose weight/burn fat, you need to consume fewer calories than your TDEE and/or increase your energy expenditure. This is called a calorie deficit or negative energy balance.
But to gain weight and build muscle, you need to consume more calories than your TDEE. This is called a calorie surplus or positive energy balance.
Alternatively, you can skip all this math and use our new TDEE calculator.
BMR Frequently Asked Questions
What does BMR mean?
BMR is an acronym for Basal Metabolic Rate. BMR is the amount of energy your body uses per 24 hours at rest and in a fasted state.
How accurate is the BMR calculator?
The three BMR equations (Mifflin St. Jeor, Revised Harris-Benedict, and Katch-McArdle) are all reasonably precise, but none of them are perfect. They are accurate estimates. The only way to precisely determine your BMR is in a laboratory setting, where things like inhaled and exhaled gases and body temperate are measured..
It’s reasonable to assume that the BMR calculator is accurate to within 10% (2). As such, you may need to modify your calorie intake depending on your actual progress.
How do I calculate my actual daily calorie expenditure?
To estimate your daily calorie needs, multiply your BMR by the relevant activity factor. This will give you your Total Daily Energy Expenditure, or TDEE for short.
How many calories should I eat per day?
Your ideal calorie intake depends on your body composition goal:
- Maintain your current weight by consuming the same number of calories as your TDEE.
- To burn fat, subtract 300-500 calories from your TDEE to create a calorie deficit.
- To gain weight or build muscle, add 300-500 calories to your TDEE to create a calorie surplus.
How often should I recalculate my BMR?
Your BMR will change if you gain muscle. It’s estimated that adding one pound of muscle to your body will increase BMR by around 50 calories per day (3). BMR also declines as you get older.
Therefore, you need to recalculate BMR from time to time. However, as changes in your BMR tend to be quite slow, there is no need to recalculate it weekly. Instead, use our calculator every month or two and adjust your calorie intake based on your latest results.
BMR Calculator – Wrapping Up
If you want to lose or gain weight, you must pay attention to your calorie intake. But, it’s not enough just to count calories; you need to know how many your body needs and then adjust your intake based on your goals.
Basal Metabolic Rate, or BMR, is the first component of your daily energy expenditure. It’s the amount of energy your body uses at rest and in a fasted state. Once you know your BMR, you can use it to estimate your TDEE or Total Daily Energy Expenditure.
Armed with your TDEE, you can add calories to gain weight and build muscle, or subtract calories burn fat and get leaner.
However, all those estimates start with your BMR, which is why this is such an important topic!
1- American Council on Exercise (ACE): BMR vs. RMR https://www.acefitness.org
2- PubMed: Comparison of predictive equations for resting metabolic rate in healthy non-obese and obese adults: a systematic review https://pubmed.ncbi.nlm.nih.gov/15883556/
3- PubMed: A high-protein diet for reducing body fat: mechanisms and possible caveats https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4258944/
4- PubMed: Effects of exercise intensity and duration on the excess post-exercise oxygen consumption https://pubmed.ncbi.nlm.nih.gov/17101527/