GDP, or gross domestic product, is the total value of goods and services produced within a country in a given year. There are three main methods to calculate GDP: the product or value added method, which sums the gross value added by each sector of the economy; the income method, which sums factor payments such as wages, interest, rent, and profits; and the expenditure method, which equals total consumption + government spending + investment + net exports in the economy. The document provides examples and formulas to demonstrate how GDP is calculated using each of these three methods.