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There are three reasons why a cash flow in the future is worth less than a similar cash flow today. People prefer consuming today to consuming in the future. Inflation decreases the purchasing power of cash over time. A dollar in the future will buy less than a dollar would today. A promised cash flow in the future may not be delivered. There is risk in waiting. The process by which future cash flows are adjusted to reflect these factors is called discounting, and the magnitude of these factors is reflected in the discount rate. The discount rate can be viewed as a composite of the expected real return (reflecting consumption preferences), expected inflation (to capture the purchasing power of the cash flow), and a premium for uncertainty associated with the cash flow. The process of discounting converts future cash flows into cash flows in today's terms. There are five types of cash flows—simple cash flows, annuities, growing annuities, perpetuities, and growing perpetuities. A simple cash flow is a single cash flow in a specified future period. Discounting a cash flow converts it into today's dollars (or present value) and enables the user to compare cash flows at different points in time. The present value of a cash flow is calculated thus:
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Aswath Damodaran (The Little Book of Valuation: How to Value a Company, Pick a Stock, and Profit (Little Books. Big Profits))