Your basal metabolic rate (BMR) is the number of calories your body burns at rest to keep you alive - powering your heart, brain, breathing, and digestion.
Knowing your BMR helps you understand your body’s energy needs so that you can make more informed choices about nutrition, exercise, and weight management.
Here, we’ll take a look at precisely what BMR is and how to calculate yours. You can also use our calculator to find yours now.
BMR is the number of calories your body uses at rest to perform essential functions.
Age, weight, body composition, hormones, and lifestyle can all affect your BMR.
Understanding your BMR helps you set realistic calorie targets for weight loss, maintenance, or fitness goals.
What is BMR?
BMR stands for Basal Metabolic Rate. It’s the number of calories your body burns at complete rest to keep you alive. This means supporting essential functions like breathing, circulation, brain activity, and digestion.
Your BMR makes up the largest part of your daily calorie use, usually up to 70% of your body’s total energy use. The rest comes from physical activity and digesting food.
BMR is not the same as RMR (Resting Metabolic Rate). RMR also measures calories burned while resting but can include small amounts of energy used for things like digesting food or sitting upright. RMR tends to be slightly higher, often around 5–10% above your BMR.
Understanding BMR is important because it gives you a baseline: the minimum calories your body needs each day before adding in movement or exercise.
What can affect your BMR?
Your BMR isn’t fixed. It changes depending on things like age, body composition, hormones, and lifestyle. These factors explain why 2 people of the same weight can burn calories at very different rates.
Key factors that influence BMR include:
Age: BMR naturally slows down as you get older, partly due to muscle loss.
Biological sex: men usually have a higher BMR because they tend to have more muscle mass.
Body composition: muscle tissue burns more calories than fat, so people with more lean muscle have a higher BMR.
Hormones: thyroid function, insulin sensitivity, and hormonal changes like menopause can all affect your BMR.
Lifestyle factors: poor sleep, high stress, and very low-calorie diets can indirectly lower BMR by affecting hormones and muscle mass.
What is considered a normal BMR?
There isn’t a single “normal” BMR because it depends on your age, sex, height, weight, and body composition.
The typical average BMR for males is around 1,700 calories a day. For females, the average BMR is around 1,400 calories.
Your BMR is very specific to you. A taller or more muscular person will usually have a higher BMR, while someone with less muscle mass or who is older may have a lower one. Online calculators can give a useful estimate, but they don’t account for medical conditions or differences in metabolism.
How to calculate BMR
You can calculate your BMR using formulas that estimate the calories your body needs at rest. The most widely used is the Mifflin-St Jeor equation, which factors in your age, sex, height, and weight.
Common methods include:
Mifflin-St Jeor Equation: the standard in most online calculators.
Harris-Benedict Equation: an older method that’s less accurate but still widely used.
online BMR calculators: these automatically apply one of the formulas when you enter your details.
It’s important to remember that BMR isn’t the same as your total daily calorie needs. To work out your TDEE (Total Daily Energy Expenditure), you need to add the calories you burn through everyday activity and exercise.
Can I estimate BMR without a calculator?
Yes, you can work out your BMR manually using standard equations. They won’t be exact, but they give a useful estimate of how many calories your body burns at rest.
The most common formula is the Mifflin-St Jeor equation:
These equations give you a baseline for calories burned at rest. Remember, this number doesn’t include physical activity.
To estimate your total daily energy needs, you’ll also need to account for your activity level.
How does BMR help with weight loss?
Knowing your BMR helps you understand how many calories your body needs at rest, which is the starting point for setting realistic weight loss goals.
By combining your BMR with your activity level, you can work out your total daily energy expenditure (TDEE).
For weight loss you’ll need to eat fewer calories than your TDEE, creating a ‘calorie deficit’ (when you use more calories than you eat in a day).
For weight maintenance aim to eat close to your TDEE.
For weight gain eat more than your TDEE, ideally from nutrient-rich foods.
People with a naturally lower BMR may find weight loss slower, but strategies like resistance (strength) training and building lean muscle can increase calorie burn and make results easier to sustain.
“While BMR and BMI are great tools for understanding your weight and body, they don’t give you the complete picture – sometimes you need to talk to a clinician. It’s also important to remember that you don’t need to make significant changes to your diet and lifestyle all at once. Make smaller changes that you know you’ll stick to first, so you can slowly build lifelong habits. That’s the key to healthy weight loss that lasts.”
Once you know your BMR, you can use it to plan a realistic calorie deficit. Start by calculating your TDEE (total daily energy expenditure), which combines your BMR with the calories you burn through daily activity and exercise.
To lose weight, you’ll need to eat fewer calories than your TDEE, typically by around 500 to 600 calories a day for steady, sustainable results.
Extreme calorie restriction isn’t recommended, as this can slow your metabolism and make it harder to keep weight off.
You can also increase the amount of calories you burn by focusing on lifestyle changes that increase your BMR. To increase your BMR, try focusing on:
Regular exercise: any physical activity boosts daily energy use, whether that’s a gentle walk or a more intense gym workout.
Building muscle: increasing lean muscle means your body burns more calories even at rest.
Eating more protein: protein helps preserve muscle while you lose fat, which helps maintain your BMR. Together, these steps make your calorie deficit easier to maintain and more effective in the long run.
Does using weight loss injections affect your BMR?
Weight loss injections like semaglutide (Wegovy) and tirzepatide (Mounjaro) don’t directly speed up your metabolism or raise your BMR. Their main effect is reducing appetite, which helps you eat fewer calories.
As you lose weight, your BMR naturally drops a little because your body has less mass to maintain. This happens with any kind of weight loss, not just injections. Some people notice their progress slows over time, but this is a normal adjustment.
The good news is you can help protect your BMR by staying active and focusing on resistance training, which builds lean muscle.
Muscle tissue burns more calories than fat, even when you’re at rest, so keeping your muscle mass up makes it easier to sustain weight loss while using injections.
BMR vs. RMR
BMR (basal metabolic rate) and RMR (resting metabolic rate) are closely related but not exactly the same. Both measure how many calories your body burns at rest, but they’re calculated under slightly different conditions.
BMR is the strictest measure. It refers to the energy your body uses in a completely rested, fasted state.
RMR is a little broader, as it can include the calories burned while doing very minimal activity, such as digesting food or sitting upright.
Because of this, RMR is usually about 5–10% higher than BMR. Most online BMR calculators actually provide an estimate of RMR, even if they use the term BMR.
Frequently asked questions
How do I increase metabolism?
You can’t change your metabolism completely, but you can support it with healthy habits. Building lean muscle through resistance exercise, staying active in daily life, getting enough sleep, and eating balanced meals with plenty of protein all help your body burn energy more efficiently.
Does Mounjaro speed up your metabolism?
No, Mounjaro (tirzepatide) doesn’t directly increase your BMR. It works by reducing appetite, helping you eat fewer calories. As with any weight loss, your BMR may fall slightly as your body mass decreases, but resistance training can help offset this change.
Is a higher BMR better?
A higher BMR simply means your body burns more calories at rest, often due to having more muscle or being taller or heavier. It’s not automatically “better” - what matters is using your BMR to understand your own energy needs and set realistic goals.
Can exercise change my BMR?
Yes - regular resistance training can raise your BMR slightly because muscle tissue burns more calories than fat. The effect isn’t huge, but it can make it easier to keep weight off long term, especially when combined with good sleep and nutrition.
Why does my BMR decrease as I lose weight?
When you lose weight, your body has less tissue to maintain, so it burns fewer calories at rest. This is a normal part of weight loss. Eating enough protein and incorporating strength training helps you maintain muscle, which can slow down this natural drop in BMR.
Does fasting affect BMR?
Short-term fasting doesn’t usually lower your BMR significantly. Long-term extreme calorie restriction, however, can slow your metabolism as your body adapts to conserve energy. This is one reason crash diets are harder to sustain compared with gradual, balanced approaches.
How accurate are BMR calculators?
Online BMR calculators are useful for estimates but aren’t 100% accurate. They use population averages, so your true BMR could be higher or lower.
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