A Calorie Calculator determines the daily calorie intake needed for weight maintenance, gain, or loss. It considers factors like age, gender, weight, height, activity level, and weight change goals. Using equations like the Mifflin-St Jeor equation, it calculates basal metabolic rate (BMR), adjusting it based on activity level and desired weight change rate. This personalized approach helps users make informed decisions about their diet and exercise, promoting healthier lifestyles and achieving fitness goals.