To “discount” the numbers back, as Buffett remarked, is the third question that proceeds from Aesop’s original “mathematics of investment”:
What’s the right discount rate?
That question is the key to evaluating the value of a company’s cash generation, and it circles back around to Buffett’s example of an investor expecting a farm to generate a 7 percent return, and basing a purchase decision on that return assumption and the current business price. There are essentially two components to the discount rate-based risk modeling: the concept of time value of money, and the additional risk premium for the investment.
The time value of money is typically accounted for using the long-term government rate. It is the way investors contend with the fact that the value of a dollar today will be lower in the future. The additional risk premium, because an investor buying a stock is taking risk versus the purchase of a bond, can be modeled by using a higher, customized discount rate, or by building what Benjamin Graham called a “margin of safety” directly into the cash flows (a concept we will come back to in the next section). For example, an investor believes there is a 90 percent probability of receiving the cash flow, they multiply the cash flow by 90 percent.
In the 1992 Berkshire Hathaway annual shareholder letter, Buffett turned to another writer, and a five-decade old business text, to explain stock value better than he thought he could himself. The text was “The Theory of Investment Value” written by John Burr Williams, a prominent figure in the history of fundamental analysis.
“The value of any stock, bond or business today is determined by the cash inflows and outflows — discounted at an appropriate interest rate — that can be expected to occur during the remaining life of the asset.”
The “remaining life of the asset” makes it difficult to specify an exact period of time for this calculation, though in an example laid out by a Berkshire Hathaway shareholder to Buffett in an exchange back in 1999 (and which we will come to later) Buffett did say that the shareholder’s model for intrinsic value looking out 20 years into the future was stated well.
Buffett went on to explain a few key differences between a discount rate for bonds and stocks. Bonds have a coupon and maturity rate that define its future cash flows. Stocks, on the other hand, are subject to cash flow estimates that even the best analysts can mess up, and, in addition, the performance of company management.
Buffett has been clear about the discount rate he prefers to use, saying at the 1996 shareholder meeting that he doesn’t think he can be very good at predicting interest rates and so he thinks in terms of “the long-term government rate,” as long as the business being considered first meets another requirement: it is one that the investor can understand. A higher discount rate is justified for riskier businesses, he said. Pertinent to the current market environment, he added: “And there may be times, when in a very — because we don’t think we’re any good at predicting interest rates, but probably in times of very — what would seem like very low rates — we might use a little higher rate.”
But this doesn’t mean Buffett is not also factoring a risk premium into his models. A “margin of safety” is likely built directly into his models so the additional risk premium is not required as a separate discount modeling rate.