A calorie calculator is a tool that estimates the number of calories needed each day to maintain, lose, or gain weight based on an individual's age, gender, weight, height, and activity level. The calculator uses a mathematical formula to determine an individual's Basal Metabolic Rate (BMR), which is the number of calories required to maintain basic bodily functions at rest, and then multiplies this number by a factor that takes into account the individual's level of physical activity.

Using a calorie calculator can help individuals make informed decisions about their food intake and help them achieve their weight goals. For example, if someone wants to lose weight, they can input their information into a calorie calculator to find out how many calories they need to consume each day to achieve their goal. Additionally, a calorie calculator can also help individuals understand how many calories they need to consume to maintain their weight or gain weight if necessary.