Calculus is a branch of mathematics that helps us understand changes between values that are related by a function. For example, given a formula indicating how much money one gets every day, calculus would help one understand related formulas, such as how much money one has in total, and whether one is getting more or less money than before. Many of these formulas are functions of time, and one way to think of calculus is to see it as a study of functions of time.