Gym-lore states that you need to eat more food if you want to gain weight. Conversely, to lose weight or burn fat, you need to eat less. And while these instructions are not incorrect, they are pretty vague. Eating more or eating less is no guarantee of success as the amount of food you consume is crucial.
For best results, you need to know how many calories your body burns per day. That number is your Active Metabolic Rate, or AMR, the same figure as your total daily energy expenditure (TDEE). Once you know it, you can make precise adjustments to build muscle or burn fat.
AMR Calculator
Example: 170 lb man, 30, lightly active
2,759calories a day
What you burn in a day: your BMR plus what your activity adds.
Eat about this much and your weight should hold; check it against the scale over two or three weeks. It is the same number our TDEE calculator gives, and the one our calorie deficit and weight gain calculators start from. Enter your own details above to replace this example.
BMR
1,721
Calories at complete rest, by the Mifflin-St Jeor equation.
Added by activity
+1,038
Lightly active: your AMR is about 1.6 x your BMR.
Every row uses your BMR of 1,721. Pick the row that matches a normal week; on rest days you burn closer to the rows above it.
| Your AMR at each activity level | Calories |
|---|---|
| SedentaryLittle or no exercise; about BMR x 1.54 | 2,655 |
| Lightly activeExercise 1 to 3 days a week; about BMR x 1.6; your choice | 2,759 |
| Moderately activeExercise 3 to 5 days a week; about BMR x 1.66 | 2,863 |
| Very activeHard exercise 6 to 7 days a week; about BMR x 1.77 | 3,049 |
| Extra activeAthlete or physical job; about BMR x 1.96 | 3,367 |
- Next stepTDEE calculatorWhere this number comes from: our main daily calorie calculator.
- Next stepCalorie deficit calculatorEat below your AMR to lose fat: a daily target and a date.
- Next stepWeight gain calculatorEat above it to gain: a surplus sized for your lifting.
- Next stepMacro calculatorSplit your calories into protein, fat and carbs.
Your AMR is your BMR, the calories you burn at complete rest, multiplied by an activity factor. We work out your BMR with the Mifflin-St Jeor equation from your weight, height, age and sex, or from your lean mass if you enter your body fat. If you leave body fat blank and you are 19 or over, the day's total comes from the National Academies' 2023 energy equation, the one our TDEE calculator uses, and the factor shown is that total divided by your BMR. If you enter your body fat, or you are under 19, we multiply your BMR by 1.2, 1.375, 1.55, 1.725 or 1.9, from sedentary to extra active. Treat your AMR as an estimate and check it against the scale.
Sources: National Academies, Dietary Reference Intakes for Energy, 2023; Mifflin and St Jeor, Am J Clin Nutr 1990
What is AMR?
Fitness and nutrition experts love their abbreviations. Hearing two fitness people talking is like listening to a conversation in code! Knowing what these abbreviations mean will make learning about fitness, exercise, training, and nutrition much easier.
So, AMR is short for Active Metabolic Rate. In simple terms, your AMR is the number of calories you burn in 24 hours, including an allowance for exercise. It is the same quantity as your total daily energy expenditure, or TDEE. Some sites call it your actual metabolic rate or daily calorie burn.
Your AMR includes the energy you use to power metabolic functions, like breathing, pumping blood around your body, brain function, etc., as well as planned and unplanned physical activity.
The calories you would burn lying still all day are your Basal Metabolic Rate, or BMR. You can estimate it with our BMR calculator.
How is AMR Calculated?
The classic way to work out your AMR takes two steps: estimate your BMR with an equation such as Mifflin-St Jeor, then multiply it by an activity factor.
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
Textbook activity factors
The textbook factors are:
- 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 3 to 5 days per week)
- Very active = BMR x 1.725 (hard exercise 6 to 7 days per week)
- Extra active = BMR x 1.9 (an athlete’s training schedule, or a physical job)
What our calculator does
Our calculator gives you the same daily total as our TDEE calculator. For adults 19 and over, that total comes from the 2023 National Academies energy equation, which researchers built from measurements of the calories people burned in daily life. If you add your body fat percentage, the calculator works out your BMR from your lean mass with the Katch-McArdle formula and multiplies that by your activity factor. Under 19, it multiplies your Mifflin-St Jeor BMR by your activity factor. The factor beside each level in your result is your total divided by your BMR. For adults it comes out higher than the textbook figure above, most of all for sedentary and lightly active people, because the 2023 equation was built from measured daily burn rather than from a multiplier.
While you COULD work all this out by hand, you don’t need to. Our AMR calculator does all the heavy lifting for you, so you don’t have to strain your brain!
How To Use The AMR Calculator
Our AMR calculator is incredibly easy to use. Just follow these step-by-step instructions, and you’ll have your results in seconds…
- Enter your weight and choose pounds or kilograms
- Enter your height: feet and inches with pounds, centimeters with kilograms
- Enter your age and choose your sex
- Pick the activity level that matches a normal week
- If you know your body fat percentage, add it with the link under the button (optional)
- Press “Work out my AMR”
Your results should appear almost instantly. If a value is missing or outside the range the calculator accepts, a message under that box tells you what to enter.
What Do the Results Mean?
Your AMR is the number of calories your body uses per day, including exercise. Your result also shows your BMR, the calories added by activity (your AMR minus your BMR), and your AMR at each of the five activity levels.
If, for example, your AMR is 2,450 calories, that is our estimate of what your body burns in a day. Eating about 2,450 calories a day should hold your weight steady. Check it against the scale over two or three weeks, and adjust if your weight moves.
Factors that may affect your AMR include:
- Muscle mass: the more muscular you are, the more calories your body uses at rest, but the gain is small. A pound of muscle burns about 6 calories a day at rest (3), so 5 lb of new muscle adds about 30 calories a day. Your daily activity changes your AMR far more.
- Age: AMR tends to decline with age, often because of decreases in muscle mass. Lost muscle is one of the factors that lead to middle-age weight gain.
- Genetics: some people have a higher AMR than others and are said to have a “fast metabolism.”
- Weather: cold weather tends to increase AMR 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 AMR as more energy is required by the growing fetus. Menopause also affects AMR and can cause it to increase or decrease depending on hormonal changes.
- Supplements and drugs: stimulants can cause AMR to increase, including caffeine. Other medications can cause the AMR to fall, such as some sedatives.
- Activity levels: as AMR includes calories burned during exercise, the more physical activity, the higher the value will be. Conversely, if you do less physical activity, your AMR will be lower. As such, you should adjust your food intake according to the amount of activity on a given day. For example, you may choose to eat less on a rest day.
The calculator works from your weight, height, age, sex, activity level and, if you add it, your body fat. It cannot see the other factors on this list, so the scale is your final check.
How to Use Your AMR
Once you know your AMR, you can use it to determine how many calories you should consume per day to achieve your weight and body composition goals.
To get leaner and lose weight, you need to lower your calorie intake to 300-500 below your AMR. This will create a calorie deficit or negative energy balance, forcing your body to burn stored body fat for fuel. A deficit of 300 to 500 calories a day adds up to 2,100 to 3,500 a week: about 0.6 to 1 pound (0.3 to 0.45 kg) of fat a week, at roughly 3,500 calories per pound (7,700 per kg). Our calorie deficit calculator sizes the gap for your goal.
To build muscle and gain weight, you need to raise your calorie intake above your AMR. This will create a calorie surplus or positive energy balance. Your body will use these extra calories for workout recovery and muscle growth. Our weight gain calculator sizes the surplus for you.
Note: these calorie recommendations are only guidelines. You may need to raise or lower them depending on your progress.
Tracking Your Calorie Intake
If you’ve taken the time to calculate your Active Metabolic Rate, you also need to track your food intake to ensure you are consuming the correct number of calories for your goal, i.e.:
- About your AMR to MAINTAIN your current weight
- Below your AMR to LOSE weight and burn fat
- Above your AMR to GAIN weight and build muscle
The easiest way to track your food intake is to use an app on your phone or tablet. There are simple, free food trackers as well as paid versions that are packed with features, such as variable macros, goal setting, in-depth nutritional breakdowns, and even customizable eating plans.
Alternatively, you can just use an online food database and work everything out for yourself.
While weighing and measuring your food can be time-consuming at first, it does get easier because most people eat the same meals several times a week. So, for example, you might have the same breakfast every day. While working out the calories in a new meal is a little laborious, so long as you save the information, you won’t have to calculate it again.
What About Macros?
The calories in your food come from a combination of proteins, carbohydrates, and fats. These food groups are collectively called the macronutrients, or macros for short. Macro means big.
While all three macros are important, changing the amount you eat of each one may help you achieve your body composition goal faster.
For example, cutting carbs and eating more protein may speed up fat loss (1). In contrast, building muscle is usually easier if you consume an abundance of protein.
So, once you know your AMR, you should then determine how many calories of proteins, carbohydrates, and fats you need to eat for the best results.
Options include:
Use our Macro Calculator to determine the best macro ratio for your training goals.
AMR FAQs
What does AMR mean?
AMR is short for Active Metabolic Rate. It’s the amount of energy your body uses per day in calories, including what’s needed for physical activity and exercise. It’s your BMR (Basal Metabolic Rate) multiplied by an appropriate activity factor. The more active you are, the higher your AMR will be.
How Accurate is the AMR calculator?
For adults, this calculator gives the same daily total as our TDEE calculator, from the 2023 National Academies energy equation. Your BMR comes from Mifflin-St Jeor, or from Katch-McArdle if you add your body fat. A 2005 review found Mifflin-St Jeor the most reliable of the common BMR equations: it came within 10% of measured resting energy for more people than any other (2).
Every equation is an estimate, so monitor your progress and adjust your calorie intake to your results. The only completely accurate way to measure AMR is in a laboratory.
How often do I need to recalculate my AMR?
Your AMR will change if you gain muscle. At rest, a pound of muscle burns about 6 calories a day and a pound of fat about 2 (3), so 5 lb of new muscle adds roughly 30 calories a day. AMR also declines with age. As such, you will need to recalculate AMR from time to time.
However, changes in your AMR happen relatively slowly, so there is no need to recalculate it daily or weekly. Instead, use our AMR calculator every month or two and adjust your calorie intake based on your most recent results.
How many calories should I eat per day?
Your ideal calorie intake depends on your body composition goal:
- Maintain your current weight by eating about as many calories as your AMR, then check it against the scale over two or three weeks.
- To burn fat, eat below your AMR. Our calorie deficit calculator sizes the gap.
- To gain weight or build muscle, eat above your AMR. Our weight gain calculator sizes the surplus.
Wrapping Up
You are what you eat, or so the old saying goes. And while that’s 100 percent true, you are also how MUCH you eat! After all, your body needs calories as well as protein, carbohydrates, fats, fiber, vitamins, and minerals. Calories are energy.
Your calorie intake needs to reflect both your needs and your goals. Consume too many, and you may gain fat or struggle to lose weight. But, consume too few, and you could undermine your workouts and struggle to build muscle.
Use our Active Metabolic Rate calculator to determine how many calories your body needs per day, and adjust your intake according to your workout and fitness goals.
References:
1- PubMed: A high-protein diet for reducing body fat: mechanisms and possible caveats https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4258944/
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: Specific metabolic rates of major organs and tissues across adulthood: evaluation by mechanistic model of resting energy expenditure https://pubmed.ncbi.nlm.nih.gov/20962155/
