Revenue is the amount of money a company receives during a period, including discounts and returns. It is the top line or gross income before subtracting costs. There are three types of revenue: total revenue, which is total receipts from sales; average revenue, which is total revenue divided by quantity sold; and marginal revenue, which is the change in total revenue from selling one more unit. Marginal revenue is calculated by subtracting total revenues with different quantities sold. Total revenue is calculated by multiplying price and quantity. Average revenue is either price under perfect competition or declines under imperfect competition as more is produced.