Discounted cash flow (DCF) valuation is used to evaluate the investment-worthiness of a stock. If the value derived from DCF valuation is higher than the current market price, the opportunity might be worth considering. Discounted Cash Flow valuation uses future free cash flow streams and discounts them (using a risk free rate + risk premium) to arrive at the present value.

However, the value of the discounted cash flows is quite different from company to company. In present value terms, CycliCorp is worth about $2700 less than StableCorp. That's because StableCorp is more predictable, which means that investors' discount rate isn't high. CycliCorp's cash flow increases by 20 percent some years and shrinks in some years, so investors perceive it as a riskier investment and use a higher discount rate when they are valuing its shares. As a result the present value of the discounted cash flows is lower.

Pat Dorsey, Director of Stock Analysis, Morningstar Inc. in his very useful book - The 5 Rules for Successful Stock Investing - tells us about discounted cash flows (DCF) how we can go about calculating them.

What is a stock worth? Economists Irving Fisher and John Burr Williams answered this question for us more than 60 years ago. The value of a stock is equal to the present value of its future cash flows. No more and no less.

Companies create economic value by investing capital and generating a return. Some of that return pays operating expenses, some get re-invested in the business, and the rest is free cash flow. Remember we care about the free cash flow because that's the amount of money that could be taken out of the business each year without harming its operations. A firm could use free cash flow to benefit shareholders in a number of ways. It can pay a dividend, which essentially converts a portion of each investor's interest in the firm to cash. It can buy back stock, which reduces the number of shares outstanding and thus increases the percentage ownership of each shareholder. Or, the firm can retain the free cash flow and re-invest it in the business.

These free cash flows are what give the firm its investment value. A present value calculation simply adjusts those future cash flows to reflect the fact that money we plan to receive in the future is worth less than money we receive today.

Why are future cash flows worth less than the current ones? First, money that we receive today can be invested to generate some kind of return, whereas we cant invest future cash flows until we receive them. This is the time value of money. Second, there is a chance that we may never receive those future cash flows, and we need to be compensated for that risk, called the risk premium.

The time value of money is essentially the opportunity cost of receiving money in the future versus receiving it today, and is often represented by the interest rates being paid on government bonds. Its pretty certain that the government will be around to pay us our interest in a few years.

Of course, not many cash flows are as certain as those from the government, so we need to take an additional premium to compensate us for the risk that we may never receive the money we have been promised. Add the government bond rate to the risk premium, and we have what's known as a discount rate.

Now you can start to see why stocks with stable, predictable earnings often have such high valuations - investors discount their future cash flows at a lower rate, because they believe that there's a lower risk attached to the likelihood that those future cash flows will actually show up. Conversely a business with an extremely uncertain future should logically have a lower valuation because there is a substantial risk that the potential future cash flows will never materialise.

You can see why a rational investor should be willing to pay more for a company that's profitable now relative to one that promises profitability only at some point in the future. Not only does the latter carry a higher risk (and thus a higher discount rate), but the promised cash flows won't arrive until some years in the future, diminishing their value still further.

Changing discount rates and the timing of cash flows can have a telling effect on present value. In all three examples, below -StableCorp, CycliCorp, and RiskCorp -the sum of the undiscounted cash flows is about $32000.

However, the value of the discounted cash flows is quite different from company to company. In present value terms, CycliCorp is worth about $2700 less than StableCorp. That's because StableCorp is more predictable, which means that investors' discount rate isn't high. CycliCorp's cash flow increases by 20 percent some years and shrinks in some years, so investors perceive it as a riskier investment and use a higher discount rate when they are valuing its shares. As a result the present value of the discounted cash flows is lower.

The difference in the present value of the cash flows is even more acute when you look at RiskCorp, which is worth almost $8300 less than StableCorp. Not only are the bulk of RiskCorp's cash flows far off in the future, bu also, we are less certain that they will come to pass, so we assign an even higher discount rate.

This is the basic principle behind a discounted cash flow model. Value is determined by the amount, timing, and riskiness of a firm's future cash flows, and these are the three items you should always be thinking about when deciding how much to pay for a stock. That's all it really boils down to.