A calorie calculator estimates the number of calories a person needs each day to maintain, lose, or gain weight. It takes into account factors such as age, sex, height, weight, and activity level to calculate your Total Daily Energy Expenditure (TDEE), which is the total number of calories burned per day including both basal metabolic rate (calories burned at rest) and calories burned during activity. From this number, one can adjust calorie intake goals for weight loss, maintenance, or gain. There are various formulas underlying calorie calculators, including:

• The Harris-Benedict Equation
• The Mifflin-St Jeor Equation (considered more accurate)
• The Katch-McArdle Formula (adjusts for lean body mass)

Many calorie calculators also provide insights into Body Mass Index (BMI), macronutrient distribution, and sample meal plans based on calorie needs. They are widely used to tailor nutrition plans and understand energy expenditure. If desired, the calculator can also factor in activity levels ranging from sedentary to very active for a more personalized estimate of energy needs. Examples of activity levels include light activity such as walking, moderate activity like jogging, or vigorous exercise like swimming or running. In summary, a calorie calculator helps people estimate their daily calorie needs to guide diet and fitness goals effectively.