The body needs energy from food to maintain vital functions and daily activities. When consumed, food is converted into calories – a unit of energy. If more calories are expended than absorbed, the body will lose weight. Therefore, to lose weight effectively, understanding how to calculate calories for weight loss is crucial, helping to scientifically control energy intake and expenditure. This is a foundational step to build a suitable diet, protect health, and achieve an ideal physique.
What are Calories? Why are calories important for the body?
Calories are units used to measure the energy the body receives through food or burns through physical activity. In nutrition, “calorie” is often understood as “kilocalorie” (kcal) – representing the energy provided by food. 1 kcal is equivalent to 1,000 “small” calories – the amount of energy needed to heat 1g of water by 1°C under standard pressure.
Each type of food provides a specific amount of calories, derived from three main macronutrient groups:
- 1g of carbohydrate provides 4 calories
- 1g of protein also provides 4 calories
- 1g of fat produces 9 calories
After eating, the body converts food into energy to fuel all life activities, from metabolism, respiration, muscle movement, to even at rest. If the absorbed calories exceed the consumed needs, the body will store them as fat – affecting weight management and long-term health.
To maintain an ideal muscle-to-fat ratio and overall health, calculating calorie consumption is essential. A common method is to apply the BMR (Basal Metabolic Rate) formula to determine the body’s minimum energy requirements at rest. Subsequently, depending on your activity level and fitness goals (weight loss, weight gain, weight maintenance), you can adjust your calorie intake.
For example, to effectively burn calories for fat loss, you need to create a calorie deficit – meaning the amount of calories expended must be greater than the calories consumed. Conversely, if you want to gain muscle, you need to consume excess calories along with exercise.
When Should You Learn How to Calculate Your Calorie Intake?
Calculating your calorie intake is an important step if you want to maintain, lose, or gain weight scientifically. This is because weight not only affects appearance but also has a significant impact on overall health, especially the risk of chronic diseases such as diabetes, obesity, and cardiovascular disease.
To determine your ideal weight, you should measure your Body Mass Index (BMI) using the formula:
BMI = Weight (kg) / Height² (m)
Example: A person who is 1.67m tall and weighs 64kg will have a BMI of 22.9 (kg/m²). According to the IDI & WPRO BMI classification table (applicable to Asians), this is a normal level, but already close to overweight:
| Classification | WHO BMI (kg/m²) | IDI & WPRO BMI (kg/m²) |
| Underweight/Thin | Below 18.5 | Below 18.5 |
| Normal | 18.5 – 24.9 | 18.5 – 22.9 |
| Overweight | 25 – 29.9 | 23 – 24.9 |
| Obesity Class I | 30 – 34.9 | 25 – 29.9 |
| Obesity Class II | 35 – 39.9 | ≥ 30 |
| Obesity Class III | ≥ 40 | — |
Note: The WHO BMI index is not entirely suitable for the physique of Vietnamese people. Therefore, it is preferable to use the IDI & WPRO BMI index for a more accurate assessment.
Once you know your BMI, you can easily calculate the daily calorie intake needed to achieve your goals: gaining weight, losing weight, or maintaining a stable weight.
Weight Loss
If you are overweight or obese, weight loss is necessary to reduce the risk of chronic diseases. In this case, your calorie intake must be lower than your daily calorie expenditure.
Example: A person who needs 2,000 calories/day and wants to lose weight should aim for a calorie intake of approximately 1,500 – 1,700 calories/day for weight loss.
The ideal calorie deficit for safe weight loss is approximately 300 – 500 calories/day. This method of calculating the necessary calorie intake for weight loss is recommended by experts as it ensures effectiveness without causing fatigue.
Weight Maintenance
If you have reached a normal weight, calorie counting helps you maintain a stable physique and prevent weight regain. Measure your calories and monitor your daily calorie expenditure to achieve a suitable balance.
Weight Gain
For underweight/thin individuals, weight gain requires a higher calorie intake than calorie expenditure. For example, a person who needs 2,000 calories/day should consume approximately 2,500 calories/day to gain about 0.5kg in 7-8 days.
How to Calculate Calories for Weight Loss
To begin a scientific weight loss journey, a clear understanding of how to calculate your calorie intake is essential. One of the most effective supporting tools is the calculation of BMR and TDEE — two crucial indicators that determine the necessary calorie amount to maintain weight or to reduce for weight loss.
BMR – The Foundation of Metabolic Activity
BMR (Basal Metabolic Rate) is an indicator of the minimum calories your body needs each day to maintain basic metabolic activities, including:
- Respiration
- Blood circulation
- Digestion
- Cell regeneration and repair
- Hormone regulation
- Maintaining body temperature stability
One of the most popular and reliable BMR calculation formulas today is the Mifflin-St. Jeor Equation:
- Men: (10 x weight(kg)) + (6.25 x height(cm)) – (5 x age) + 5
- Women: (10 x weight(kg)) + (6.25 x height(cm)) – (5 x age) – 161
Example: A 30-year-old male, 170cm tall, weighing 70kg has a BMR of:
(10×70) + (6.25×170) – (5×30) + 5 = 1617.5 calories/day
TDEE – Total Daily Energy Expenditure
After calculating BMR, you can easily calculate TDEE (Total Daily Energy Expenditure) using the formula:
TDEE = BMR x AF, where AF (Activity Factor) is your activity level.
| Activity Level | Description | AF |
| Sedentary | Little to no exercise | 1.2 |
| Lightly Active | Exercise 1–3 times/week | 1.375 |
| Moderately Active | Exercise 3–5 times/week | 1.55 |
| Very Active | Exercise 6–7 times/week | 1.725 |
| Extremely Active | Exercise >90 minutes/day or heavy labor | 1.9 |
Example: For the male mentioned above, if lightly active 1–3 days/week:
TDEE = 1617.5 x 1.375 = 2224 calories/day
Based on the above result, if this person wants to maintain their weight, they need to consume approximately 2224 calories per day. To lose weight, they can reduce their intake by 300–500 calories from their TDEE, depending on their goal.
While you can certainly calculate calories for weight loss at home, for accurate data on body composition (fat, muscle, water percentage, etc.), consider getting a body analysis using an InBody machine at reputable medical centers or nutrition clinics.
Calorie Consumption Chart by Age and Gender
Determining appropriate energy needs based on age, gender, and physical activity is a key factor in ensuring comprehensive health for Vietnamese people. Based on the nutrition recommendations from the National Institute of Nutrition, Ministry of Health, daily calorie consumption levels are adjusted for each developmental stage as follows:
| Age Group | Men (kcal/day) | Women (kcal/day) |
| Light | Average | |
| 0–5 months | – | 550 |
| 6–8 months | – | 650 |
| 9–11 months | – | 700 |
| 1–2 years | – | 1000 |
| 3–5 years | – | 1320 |
| 6–7 years | 1360 | 1570 |
| 8–9 years | 1600 | 1820 |
| 10–11 years | 1880 | 2150 |
| 12–14 years | 2200 | 2500 |
| 15–19 years | 2500 | 2820 |
| 20–29 years | 2200 | 2570 |
| 30–49 years | 2010 | 2350 |
| 50–69 years | 2000 | 2330 |
| ≥ 70 years | 1870 | 2190 |
Pregnant and breastfeeding women need to add to their normal calorie consumption:
- First trimester of pregnancy: +50 kcal/day
- Second trimester of pregnancy: +250 kcal/day
- Third trimester of pregnancy: +450 kcal/day
- Lactation period: +500 kcal/day
Factors Determining Accurate Calorie Calculation
Accurate calorie counting plays a pivotal role in the journey of weight loss or physique maintenance. However, the amount of calories each person’s body needs is not fixed but varies depending on many individual factors. Below are the factors that strongly influence the body’s energy consumption and calorie-burning capacity.
Activity Level
The more physical activity you do, the higher the amount of calories burned. This is a factor that can change daily and directly impacts the creation of a calorie deficit – a mandatory condition for fat loss. For instance, a person weighing 68kg cycling for 1 hour at 20km/h can burn over 500 calories. Beyond expending energy, exercise also helps build an optimal muscle-to-fat ratio, supporting more efficient metabolic function.
Height and Weight
Height and weight are fundamental metrics used to estimate BMR (Basal Metabolic Rate) – the basic energy level needed to sustain vital functions. Larger individuals typically require more energy, even when not physically active. Correctly applying the BMR formula helps personalize dietary plans, ensuring appropriate and safe energy consumption.
Age
As people age, the body’s natural metabolic rate gradually declines. This decline is accompanied by muscle mass loss and reduced physical activity, leading to a lower muscle-to-fat ratio. Consequently, older individuals typically require fewer calories than younger ones. Therefore, adjusting calorie calculation methods to suit different age groups is essential to ensure effective weight management.
Gender
Men and women have different biological structures, particularly regarding muscle mass and hormones. Men generally have higher muscle mass, which helps them consume energy more efficiently both at rest and during activity. In contrast, women tend to store fat more easily and find it harder to gain muscle, leading to lower calorie needs. This is why gender is an important factor to consider in BMR calculation formulas like Mifflin-St Jeor or Harris-Benedict.
Warning: Calorie-Rich Foods That Easily Cause Weight Gain
When losing weight, accurate calorie counting is the foremost important factor. Some calorie-rich foods, even consumed in small amounts, can quickly cause weight gain, especially if intake is not controlled. Furthermore, many of these foods are low in micronutrients and can even negatively impact health.
Fatty meats: These are “hidden” calorie sources that are hard to recognize. Just 100g of pork belly can contain over 500 calories, mostly from unhealthy fats. In contrast, the same amount of lean meat only has about 143 calories and is rich in protein – a nutrient that promotes satiety and muscle maintenance.
Fried foods: Dishes like fried chicken wings, french fries, etc., are appealing but contain large amounts of oil and fat. On average, 100g of fried chicken wings provides 230 to 460 calories, along with many seasonings and saturated fats, which negatively affect the cardiovascular system and easily lead to weight gain.
Sweets and pastries: Cookies, candies, and other sweet treats contain a lot of sugar – a factor that causes rapid blood sugar spikes after eating. While they provide a lot of energy, sugar does not help the body feel full for long, lacks micronutrients, and can easily lead you to exceed your calorie needs.
Sugary drinks: Milk tea, sodas, bottled juices, etc., are “hidden culprits.” A 330ml can of soft drink can contain about 150 calories, mostly from simple sugars that offer no health benefits. Frequent consumption will slow down the weight loss process.
Processed foods and high-fat dishes: Items like instant noodles, canned goods, richly seasoned stir-fries, etc., often contain very high calories with little protein or micronutrients. They can easily lead to weight gain if portion sizes are not controlled.
Important Notes When Eating a Calorie-Reduced Diet for Safe Weight Loss
When implementing a calorie-reduced diet for weight loss, in addition to understanding how to calculate calorie deficit, you need to pay attention to health factors to avoid negative impacts on your body:
You should not cut too many calories in a day, as this can lead to fatigue, physical debilitation, and nutrient deficiencies, severely impacting your immune system and daily work performance.
Limit over-exercising. When the body lacks sufficient energy, excessive physical activity can lead to muscle damage, joint injuries, making the body’s recovery process more difficult and easily causing prolonged injuries.
Always fully account for all calorie sources, including: main meals, beverages, fruits, and even small snacks. Many people often overlook these “hidden” calories, which can impact their weight loss plan.
During the weight loss process, if you experience dizziness, fatigue, or reduced work efficiency, you should visit a reputable medical facility for timely advice and adjustment of your diet.
Common Mistakes When Calculating Calories for Weight Loss That Make It Hard to Reach Your Goals
Accurate calorie counting for weight loss plays an important role in the journey to regain your physique. However, many people still make basic mistakes, which seriously affect their health and weight loss effectiveness.
Excessive Daily Calorie Restriction
Many people believe that the more calories they cut, the faster they will lose weight, but this is a common misconception. A severe calorie deficit will leave the body lacking energy for daily activities. Furthermore, the fat loss process takes time for the body to convert fat into energy – slower than when using food. Therefore, it is better to maintain a safe calorie deficit rather than cutting too abruptly.
Failing to Ensure Nutritional Balance
A diet that completely eliminates carbohydrates or fats can lead to metabolic disorders and impaired physiological functions. In reality, both carbohydrates and fats are essential for metabolism, hormonal balance, and nerve function. When your diet is imbalanced, you may experience fatigue, hormonal imbalances, especially an increase in the hormone cortisol – which causes the body to store more fat.
Losing Weight Too Quickly in a Short Period
Safe weight loss cannot be rushed. Rapid weight loss not only debilitates the body but also slows down metabolism, causes nutrient deficiencies, increases the risk of gallstones, and leads to psychological disorders. Furthermore, when hormones like cortisol are elevated, you will be more prone to cravings and lose control. Effective weight loss should combine fat loss with muscle building, along with a nutritionally complete diet and appropriate exercise.
Properly understanding and effectively applying calorie counting for weight loss is the initial foundation. However, to achieve sustainable results, you need to maintain a scientific diet, balance energy intake and expenditure, along with patience and a clear roadmap.
