How to Calculate Percentage. Calculating percent is a fundamental math skill, whether you're taking a class or just living life! Percentages are used to make car and house payments, calculate tips and pay taxes on goods. Percent calculations are fundamental to many classes, especially science courses. This app has a step-by-step tutorial on how to calculate percent. The word percentage comes from the word percent. If you split the word percent into its root words, you see “per” and “cent.” Cen