A calorie is a unit of energy that quantifies the energy your body derives from food and uses to fuel every bodily function. Determining your daily caloric need is the first step in managing weight. This goal number is known as your Total Daily Energy Expenditure (TDEE), which accounts for the calories burned simply existing and the energy expended through physical activity. For an individual weighing 120 pounds, calculating TDEE provides a specific starting point for estimating energy requirements.
Determining Your Baseline Calorie Requirement
The foundation of your TDEE is the Basal Metabolic Rate (BMR), which represents the minimum number of calories your body needs to perform life-sustaining functions while at complete rest. This energy is used for processes like breathing, circulating blood, and regulating body temperature. BMR accounts for approximately 60% to 70% of the average person’s total daily calorie burn.
The Mifflin-St Jeor equation is a widely accepted formula for estimating BMR, taking into account weight, height, age, and sex. For calculation, 120 pounds converts to approximately 54.5 kilograms. For a hypothetical 30-year-old woman who is 5 feet 4 inches tall (162.5 cm), the BMR would be approximately 1,280 calories per day. This is calculated using the formula: (10 x 54.5 kg) + (6.25 x 162.5 cm) – (5 x 30 years) – 161.
This BMR figure is a static number, representing the minimum energy burned even on a day spent entirely in bed. It provides a minimum calorie floor but does not account for calories burned through daily movement or exercise. Age and sex are included in the equation because they influence metabolic rate, as muscle mass requires more energy at rest.
The Role of Activity Level
To transition from the static BMR to the Total Daily Energy Expenditure (TDEE), the baseline figure is multiplied by an activity factor. This factor quantifies daily movement and is the largest variable that personalizes the calorie estimate. Standard multipliers range from 1.2 for a sedentary lifestyle to 1.9 for an extremely active one.
A sedentary lifestyle, involving little to no exercise, uses a multiplier of 1.2. A light activity level, involving exercise one to three days per week, corresponds to a multiplier of 1.375. A moderate activity level, which includes exercising three to five days a week, uses a factor of 1.55.
For a 120-pound individual with a BMR of 1,280 calories, the difference between activity levels is substantial. A sedentary individual would have a TDEE of about 1,536 calories (1,280 x 1.2). If that same person is moderately active, their TDEE rises to approximately 1,984 calories (1,280 x 1.55). Accurately assessing your routine is necessary for a meaningful TDEE estimate.
Adjusting Intake for Weight Loss or Gain
The calculated TDEE represents the number of calories needed to maintain the current body weight of 120 pounds. Achieving a specific weight goal requires creating a consistent energy imbalance: a calorie deficit for weight loss or a calorie surplus for weight gain. Weight change occurs when calories consumed do not equal calories expended.
For moderate weight loss, creating a daily calorie deficit of approximately 500 calories below the TDEE is recommended. This deficit aims for a sustainable weight loss rate of about one pound per week, as one pound of body fat is roughly equivalent to 3,500 calories. For example, if the maintenance TDEE is 1,984 calories, the daily intake goal for weight loss would be reduced to about 1,484 calories.
Conversely, individuals aiming for weight gain, such as building muscle, should consume a moderate calorie surplus. A daily surplus of 250 to 500 calories above the TDEE supports new tissue growth while minimizing fat storage. Tracking weekly weight changes is necessary to determine if the initial goal is working, as metabolic responses vary and adjustments may be required.
Calorie Quality Matters More Than Quantity
While weight change relies on total caloric balance, the source of those calories significantly impacts the body’s internal processes and overall feeling of satiety. Consuming 1,800 calories from highly processed foods produces a different physiological effect than the same number of calories from whole, nutrient-dense foods. The quality of food influences hormonal balance, which regulates hunger and appetite.
Protein and fiber are two components of food quality that affect satiety and metabolism. Protein requires more energy to digest and process—known as the Thermic Effect of Food—and helps preserve muscle mass during a calorie deficit. Fiber, found in whole foods, slows digestion and stabilizes blood sugar, preventing hormonal fluctuations that trigger hunger and cravings. Focusing on whole foods supports stable energy levels and better hormonal signaling, making adherence to a specific calorie target manageable.