Calories In vs Calories Out: Simple Guide to Understanding Calories
Updated: Sep 10
Calories are something we hear about all the time when talking about food, fitness, weight loss and healthy eating
But what exactly is a calorie?
How many calories do we actually need each day?
What does "calories in vs calories out" really mean?
How do you work out your own calorie needs?
And does counting calories mean you have to weigh and measure everything you eat?
This guide breaks down the basics of calories, where they come from, how our bodies use them, and how calorie intake can influence maintaining, losing or gaining weight
What exactly is a calorie?
A calorie is a unit of energy.
When we talk about calories in food, we are generally referring to kilocalories, written as kcal.
Your body needs energy to keep you alive and functioning.
That energy is used for things such as:
Breathing
Pumping blood
Keeping your body warm
Brain function
Digestion
Moving your body
Exercising
Repairing and building tissues
Supporting your organs and immune system
Everyday activities such as walking, cleaning, working and shopping
Food provides the energy your body needs to perform these functions.
The amount of energy a food provides depends largely on its macronutrients:
Carbohydrates
Protein
Fat
Alcohol also provides energy, although it is not considered an essential nutrient
Where do calories come from?
The main sources of calories in food are:
Carbohydrates
Carbohydrates provide approximately 4 calories per gram.
They are found in foods such as:
Bread
Rice
Pasta
Potatoes
Oats
Cereals
Fruit
Legumes
Milk and yoghurt
Sweets and sugary foods
Carbohydrates are an important source of energy, particularly for the brain and during physical activity.
Choosing mostly minimally processed carbohydrate sources can also provide fibre, vitamins and minerals.
Protein
Protein provides approximately 4 calories per gram.
Protein is important for:
Building and repairing muscle
Maintaining body tissues
Supporting enzymes and hormones
Supporting the immune system
Helping with fullness after meals
Protein-rich foods include:
Chicken
Beef
Fish
Eggs
Greek yoghurt
Milk
Cottage cheese
Tofu
Tempeh
Beans
Lentils
Other legumes
Fat
Fat provides approximately 9 calories per gram.
Fat is more energy-dense than carbohydrates and protein.
Dietary fat is important for:
Hormone production
Cell function
Brain health
Absorption of fat-soluble vitamins
Providing energy
Helping meals feel satisfying
Sources of dietary fat include:
Avocado
Nuts
Seeds
Nut butters
Olive oil
Fatty fish
Eggs
Dairy products
Alcohol
Alcohol provides approximately 7 calories per gram.
Alcohol is not an essential nutrient.
Alcoholic drinks can also contain additional calories from sugar, mixers and other ingredients.
Calories are not the whole story
Two foods can contain a similar number of calories but provide very different amounts of nutrition.
For example, a food may provide calories but very little protein, fibre, vitamins or minerals.
Other foods can provide calories alongside:
Protein
Fibre
Vitamins
Minerals
Essential fatty acids
Other beneficial nutrients
This is why healthy eating is about more than simply hitting a calorie number.
The overall quality of your diet matters.
A nutritious diet generally includes a variety of foods from different food groups
The main food groups
A balanced diet can include foods from several major food groups
Vegetables
Vegetables provide fibre, vitamins, minerals and other beneficial plant compounds.
Examples include:
Leafy greens
Broccoli
Carrots
Capsicum
Tomatoes
Cucumber
Green beans
Pumpkin
Mushrooms
Fruit
Fruit provides carbohydrates, fibre, vitamins, minerals and other plant compounds.
Examples include:
Apples
Bananas
Berries
Oranges
Mangoes
Kiwi fruit
Grapes
Grains and cereals
Examples include:
Oats
Rice
Bread
Pasta
Couscous
Quinoa
Wholegrain cereals
Wholegrain options generally provide more fibre than refined grain products
Protein foods
Examples include:
Meat
Chicken
Fish
Eggs
Tofu
Tempeh
Beans
Lentils
Dairy foods
Dairy and alternatives
Examples include:
Milk
Yoghurt
Cheese
Calcium-fortified plant-based alternatives
Healthy fats
Examples include:
Nuts
Seeds
Avocado
Olive oil
Fatty fish
These food groups don't need to be eaten separately.
Many foods contain more than one type of nutrient.
For example, nuts contain fat and protein, while dairy foods can provide protein, carbohydrates and fat
What does "calories in vs calories out" mean?
"Calories in" refers to the energy you consume through food and drinks.
"Calories out" refers to the energy your body uses.
Your body is constantly using energy, even when you are resting.
In simple terms:
If you consistently consume roughly the same amount of energy as you use, your body weight will tend to remain relatively stable over time.
If you consistently consume more energy than you use, body weight tends to increase over time.
If you consistently consume less energy than you use, body weight tends to decrease over time.
This is often called an energy deficit or energy surplus
What makes up "calories out"?
Your daily energy expenditure is not just the calories you burn during exercise.
It includes several components
Basal metabolic rate
Your basal metabolic rate, or BMR, is the energy your body needs to maintain basic functions at rest.
This includes things such as:
Breathing
Circulation
Maintaining body temperature
Supporting your organs
Basic cellular processes
BMR makes up a significant portion of the energy most people use each day
Physical activity
This includes planned exercise such as:
Running
Walking
Cycling
Swimming
Weight training
Group fitness classes
It also includes everyday movement
Non-exercise activity
This is sometimes referred to as NEAT, or non-exercise activity thermogenesis.
It includes movement such as:
Walking around the house
Standing
Cooking
Cleaning
Shopping
Fidgeting
Moving around at work
These small movements can add up throughout the day
Thermic effect of food
Your body also uses energy to digest, absorb and process the food you eat.
Different macronutrients require different amounts of energy to process
How many calories do I need each day?
There is no single calorie number that every adult should eat.
Calorie requirements vary significantly from person to person.
Your needs can be influenced by:
Age
Sex
Height
Body weight
Muscle mass
Genetics
Activity level
Occupation
Exercise
Goals
Certain health or medical factors
This is why a calorie target that works for one person may not be appropriate for another
How to calculate your calorie needs
One common approach is to estimate your BMR and then multiply it by an activity factor to estimate your total daily energy expenditure, or TDEE.
A commonly used BMR equation is the Mifflin-St Jeor equation
For males
BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + 5
For females
BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) − 161
This gives an estimate of the energy your body uses at rest.
It is not your recommended daily calorie intake
Estimating total daily energy expenditure
Once you have estimated BMR, you can multiply it by an activity factor.
Common approximate activity categories include:
Sedentary: BMR × 1.2
Lightly active: BMR × 1.375
Moderately active: BMR × 1.55
Very active: BMR × 1.725
Extremely active: BMR × 1.9
The result is an estimate of your TDEE.
Your actual energy expenditure can be higher or lower than the calculation suggests.
Think of these formulas as a starting point rather than an exact measurement
Example calculation
Imagine a 30-year-old woman who weighs 70 kg and is 165 cm tall.
Her estimated BMR using the Mifflin-St Jeor equation would be:
BMR = (10 × 70) + (6.25 × 165) − (5 × 30) − 161
BMR = approximately 1,405 calories per day.
If she were moderately active:
1,405 × 1.55 = approximately 2,178 calories per day.
Her estimated maintenance intake could therefore be around 2,180 calories per day.
This is only an estimate.
Her actual maintenance calories could be different
How many calories should a healthy adult female eat?
There is no universal number for women.
Some adult women may maintain their weight on considerably less than 2,000 calories, while others may need considerably more.
A physically active woman with a larger body size may require substantially more energy than a smaller, sedentary woman.
Rather than asking:
"How many calories should every woman eat?"
A better question is:
"What calorie intake is appropriate for this particular woman based on her body, activity level and goal?"
How many calories should a healthy adult male eat?
The same principle applies to men.
Some men may maintain their weight on around 2,000 calories, while others may require 3,000 calories or more.
A taller, heavier or highly active man generally requires more energy than a smaller, sedentary man.
Individual calculations are therefore much more useful than a single recommended number
Calories for maintaining your weight
If your goal is to maintain your current weight, you generally want your average calorie intake to be around your average energy expenditure.
For example:
Estimated TDEE = 2,200 calories
Average intake = around 2,200 calories
Weight would generally be expected to remain relatively stable over time.
It is normal for body weight to move up and down from day to day.
Changes in:
Water
Sodium
Carbohydrates
Food volume
Hormonal changes
Digestion
Exercise
Menstrual cycle
can all affect the number on the scales
Calories for weight loss
Weight loss generally requires a sustained calorie deficit.
This means consuming less energy than your body uses over time.
For example:
Estimated maintenance = 2,300 calories
Intake = 2,000 calories
Approximate deficit = 300 calories per day
A moderate calorie deficit is often more sustainable than an extremely restrictive diet.
The goal should be to lose weight while still providing your body with enough nutrition and energy.
Weight loss will not necessarily happen at exactly the same rate every week.
Your body weight can fluctuate even when you are consistently in a calorie deficit
Calories for gaining weight
Weight gain generally requires a sustained calorie surplus.
This means consuming more energy than your body uses.
For example:
Estimated maintenance = 2,500 calories
Intake = 2,800 calories
Approximate surplus = 300 calories per day
If your goal is to build muscle, simply eating more calories is not enough.
Resistance training, adequate protein, recovery and a well-balanced diet are also important
How to measure calories in food
There are several ways to estimate calorie intake
Nutrition labels
Packaged foods usually provide nutritional information.
Depending on the country, labels may provide:
Calories or kilojoules
Protein
Carbohydrates
Fat
Saturated fat
Sugars
Fibre
Sodium
Pay attention to the serving size.
A package may contain multiple servings
Food scales
A digital kitchen scale can make calorie tracking more accurate.
You can weigh foods in grams and enter the amount into a tracking app.
This can be particularly useful when you are learning portion sizes.
It is generally more useful to think of calorie tracking as a learning tool rather than something you have to do perfectly forever
Measuring cups and spoons
These can be useful for foods that are difficult to weigh.
However, weighing food can often provide a more consistent measurement
Recipe calculations
For homemade meals, you can:
Weigh or measure each ingredient
Record the calories for each ingredient
Add the calories together
Divide the total by the number of servings
Using calorie-tracking apps
Apps such as MyFitnessPal can make tracking easier.
You can search for foods, enter portions and keep a record of your daily intake.
Many tracking apps allow you to record:
Calories
Protein
Carbohydrates
Fat
Fibre
Meals
Snacks
Drinks
Exercise
Some apps also allow you to scan product barcodes.
Other popular tracking apps are available, so it is worth finding one that is easy for you to use
How accurate are calorie-tracking apps?
Calorie-tracking apps are useful, but they are not perfect.
Some food entries are added by users and may contain errors.
Restaurant meals can be particularly difficult to estimate.
Portion sizes can also be misjudged.
Even nutrition labels have a degree of permitted variation.
Therefore, calorie tracking should generally be viewed as an estimate rather than an exact science
Do you need to count every calorie?
No.
Some people enjoy tracking because it gives them useful information and structure.
Other people find tracking stressful or unnecessary.
You can improve your nutrition without counting every calorie by focusing on:
Appropriate portions
Plenty of vegetables
Fruit
Adequate protein
High-fibre carbohydrates
Healthy fats
Mostly minimally processed foods
Eating according to hunger and fullness
Regular meals
Calorie counting is a tool, not a requirement for healthy eating
Why protein matters when managing calories
Protein can be particularly useful when trying to lose weight or build muscle.
It can help with:
Muscle maintenance
Muscle growth when combined with resistance training
Recovery
Feeling satisfied after meals
Good protein sources include:
Chicken
Fish
Lean meat
Eggs
Greek yoghurt
Cottage cheese
Tofu
Tempeh
Beans
Lentils
Why fibre matters
Fibre is found mainly in plant foods.
Good sources include:
Vegetables
Fruit
Whole grains
Beans
Lentils
Nuts
Seeds
Fibre can support:
Digestive health
Bowel regularity
Feeling full
A healthy gut
Overall diet quality
Calories and exercise
Exercise can increase the amount of energy your body uses.
Activities such as:
Walking
Running
Cycling
Swimming
Strength training
Sports
all contribute to energy expenditure.
However, exercise calorie estimates from watches, machines and apps are not always accurate.
It is generally better not to assume that you have to "eat back" every calorie an exercise tracker says you burned
Can you eat anything you want if it fits your calories?
Technically, calorie balance has a major influence on changes in body weight.
However, calories alone do not determine whether a diet is healthy.
For example, two diets could contain the same number of calories but differ greatly in:
Protein
Fibre
Vitamins
Minerals
Essential fats
Fruit and vegetable intake
Overall nutritional quality
A healthy approach is therefore to consider both:
How much energy you are consuming
Where that energy is coming from
Calorie density
Some foods contain many calories in a relatively small amount of food.
Other foods contain fewer calories in a larger volume.
Foods that tend to be more calorie-dense include:
Oils
Butter
Nuts
Nut butters
Chocolate
Pastries
Fried foods
Foods that tend to be less calorie-dense include:
Many vegetables
Some fruits
Soups
Lean proteins
Some low-fat dairy products
Understanding calorie density can help you build meals that are satisfying without unintentionally consuming very large amounts of energy
Why weight loss isn't always linear
One of the biggest misconceptions about calories is that weight should drop in a perfectly predictable straight line.
In reality, body weight can fluctuate because of:
Water retention
Sodium intake
Carbohydrate intake
Hormonal changes
Menstrual cycle
Constipation
Food still being digested
Changes in exercise
Stress
Sleep
This is why looking at a longer-term trend is usually more useful than focusing on one day's weigh-in
What if the scales aren't moving?
If someone has been consistently tracking their food and body weight has not changed for several weeks, possible explanations include:
Their calorie intake is higher than they realise
Portions are being underestimated
Drinks, sauces or snacks are being missed
Their estimated maintenance calories are lower than expected
Their activity level has changed
Water retention is masking fat loss
Their body weight is simply fluctuating
It is usually better to look at trends over several weeks rather than making drastic changes after a few days
Common calorie-counting mistakes
Forgetting cooking oils
Forgetting sauces and dressings
Underestimating portion sizes
Not counting drinks
Assuming a food labelled "healthy" is automatically low-calorie
Relying entirely on exercise tracker calorie estimates
Using an incorrect serving size
Forgetting snacks and small bites
Becoming overly focused on hitting an exact number every single day
Ignoring protein, fibre and overall nutritional quality
Do calories need to be exactly the same every day?
No.
Your energy needs can vary from day to day.
You may naturally eat more on a highly active day and less on a quieter day.
What matters more is the overall pattern over time.
For example, someone might eat:
2,000 calories one day
2,200 calories another day
1,900 calories another day
Their average intake across the week can be more meaningful than any individual day
Calories and healthy relationships with food
Tracking calories can be useful for some people, but it is not suitable for everyone.
If calorie counting causes:
Anxiety around food
Guilt after eating
Fear of certain foods
Obsessive weighing or tracking
Avoidance of social situations involving food
Extreme restriction
it may be a sign that a different approach would be healthier.
Food is more than numbers.
Eating should also be enjoyable, social and flexible
The bigger picture
Calories matter because your body requires energy.
Energy balance plays an important role in whether body weight tends to increase, decrease or remain stable.
But healthy nutrition is about much more than calories.
A balanced approach can include:
Enough calories to support your body's needs
Adequate protein
Plenty of vegetables
Fruit
Wholegrain and high-fibre carbohydrate sources
Healthy fats
Adequate hydration
Regular physical activity
Sufficient sleep
Enjoyment and flexibility
The simple takeaway
Calories are a measure of energy.
Your body needs energy every day, even when you are sleeping.
"Calories in" refers to the energy you consume.
"Calories out" refers to the energy your body uses.
Consistently eating more energy than you use tends to result in weight gain.
Consistently eating less energy than you use tends to result in weight loss.
Eating around your energy needs tends to support weight maintenance.
Individual calorie requirements vary greatly.
BMR and TDEE calculations can provide a useful starting estimate.
Food scales, nutrition labels and apps such as MyFitnessPal can help you understand your intake
Calorie tracking does not have to be perfect to be useful.
Food quality, protein, fibre, vitamins, minerals and overall dietary patterns matter too.
Exercise is valuable for far more than simply burning calories.
Sustainable habits are generally more useful than extreme restriction.
And most importantly, calories are a tool for understanding nutrition, not a reason to fear food.
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