To lose 1 pound a week, you must create a deficit of approximately 3,500 calories per week, which equals roughly 500 calories per day. This means consuming 500 calories fewer than your Total Daily Energy Expenditure, or TDEE, each day. For example, if your TDEE is 2,200 calories, your daily intake target is 1,700 calories.
The Basic Arithmetic of a Calorie Deficit
Weight loss is governed by the laws of thermodynamics. One pound of body fat contains approximately 3,500 calories of stored energy. To lose that pound, you must burn more energy than you consume over a seven day period.
Dividing the weekly target by seven yields the daily target:
- 3,500 calories per week / 7 days = 500 calories per day.
This 500 calorie daily deficit is a standard starting point. It represents an estimate, as metabolic rates and individual energy expenditure vary.
Historically, this math is known as Wishnofsky's rule, established in 1958. While modern research shows that human metabolism adapts dynamically to changes in intake, the 3,500 calorie rule remains a highly practical mathematical model for planning.
How to Calculate Your TDEE
Before you can subtract 500 calories, you must estimate your starting point. Your Total Daily Energy Expenditure, or TDEE, represents the total number of calories your body burns in a 24 hour period.
TDEE is calculated using two numbers:
- Basal Metabolic Rate (BMR): The calories your body burns at rest to maintain basic life functions.
- Activity Factor: A multiplier that accounts for physical movement, exercise, and daily tasks.
To find your TDEE, first calculate your BMR using a standard formula, such as the Mifflin-St Jeor equation. This formula uses your weight, height, age, and biological sex as mathematical variables to estimate baseline energy use. Then, multiply your BMR by the activity factor that matches your daily routine.
Activity Factor Multipliers
These standard multipliers estimate daily energy expenditure based on activity:
- Sedentary (little to no exercise): BMR multiplied by 1.2
- Lightly active (light exercise 1 to 3 days per week): BMR multiplied by 1.375
- Moderately active (moderate exercise 3 to 5 days per week): BMR multiplied by 1.55
- Very active (hard exercise 6 to 7 days per week): BMR multiplied by 1.725
For example, a person with a BMR of 1,600 calories who is moderately active would have a TDEE of 2,480 calories.
These multipliers are mathematical models. They do not account for individual variations in muscle mass, genetics, or metabolic efficiency.
Worked Example of a 1 Pound Weekly Loss
Let us look at a concrete example using average numbers. Suppose an individual has a TDEE of 2,200 calories per day.
To lose 1 pound per week, the daily calculation is:
- 2,200 calories (TDEE) - 500 calories (Deficit) = 1,700 calories (Daily Target).
Consuming 1,700 calories each day will result in a weekly deficit of 3,500 calories. You can run your own numbers in the calorie deficit calculator to estimate your baseline.
This calculation assumes your activity level remains constant. If your movement decreases, your TDEE will drop, which will reduce the actual deficit.
What if Your TDEE is Lower Than Average?
For individuals with smaller body frames, older age, or highly sedentary routines, TDEE may be lower. For instance, a small frame might have a TDEE of only 1,600 calories.
Subtracting 500 calories from a TDEE of 1,600 calories results in a daily target of 1,100 calories. Consuming fewer than 1,200 calories per day can make it difficult to meet daily nutritional requirements.
In this scenario, a smaller daily deficit is often used. A deficit of 250 calories per day targets a loss of 0.5 pounds per week. Alternatively, physical activity can be increased to raise the daily TDEE.
How Does Exercise Affect the Daily Target?
Exercise increases your daily energy expenditure, which raises your TDEE. If your sedentary TDEE is 2,000 calories, and you burn 300 calories by walking, your TDEE for that day rises to 2,300 calories.
To maintain a 500 calorie deficit on that active day, your daily intake calculation changes:
- 2,300 calories (Active TDEE) - 500 calories (Deficit) = 1,800 calories (Daily Target).
This means you can consume 1,800 calories instead of 1,500 calories while maintaining the same rate of weight loss.
However, estimating calories burned from exercise is notoriously inaccurate. Wearables often overestimate the energy cost of activity by 20 to 40 percent.
Why Does Weight Loss Speed Change Over Time?
As you lose weight, your body mass decreases. A smaller body requires less energy to move and function, which reduces both BMR and TDEE.
If your TDEE starts at 2,200 calories, it may drop to 2,100 calories after you lose 10 pounds. If you continue to consume 1,700 calories, your daily deficit shrinks to 400 calories.
This smaller deficit reduces your weekly weight loss rate. To maintain a rate of 1 pound per week, you must recalculate your TDEE periodically and adjust your daily target downward.
How Do Macronutrients Interact With the Calorie Deficit?
While the rate of weight loss is determined by the total calorie deficit, the composition of those calories affects how you feel. A daily budget of 1,700 calories can be spent on any food source, but different macronutrients have different mathematical properties.
Protein has a higher thermic effect of food than carbohydrates or fats. This means the body burns more energy digesting protein than other nutrients.
Specifically, about 20 to 30 percent of the energy in protein is lost during digestion, compared to 5 to 15 percent for carbohydrates and 0 to 3 percent for fats. This is an important variable when managing how satisfied you feel within a fixed calorie budget.
Managing Your Daily Calorie Budget
Calculating a calorie deficit is the first step in managing a daily energy budget. You can think of your daily target as a starting balance that you spend down through eating, and buy back through walking and movement.