VII. Debt Financing 24. Valuing Debt
that I know the price of apples will increase over the year by 10 percent. Then I will
part with $100 today if I am repaid $115 at the end of the year. That $115 is needed
to buy me 5 percent more apples than I can get for my $100 today. In other words,
the nominal, or “money,” rate of interest must equal the required real, or “apple,”
rate plus the prospective rate of inflation.
6
A change of 1 percent in the expected in-
flation rate produces a change of 1 percent in the nominal interest rate. That is
Fisher’s theory: A change in the expected inflation rate will cause the same change
in the nominal interest rate; it has no effect on the required real interest rate.
7
Nominal interest rates cannot be negative; if they were, everyone would prefer
to hold cash, which pays zero interest.
8
But what about real rates? For example, is
it possible for the money rate of interest to be 5 percent and the expected rate of in-
flation to be 10 percent, thus giving a negative real interest rate? If this happens,
you may be able to make money in the following way: You borrow $100 at an in-
terest rate of 5 percent and you use the money to buy apples. You store the apples
and sell them at the end of the year for $110, which leaves you enough to pay off
your loan plus $5 for yourself.
Since easy ways to make money are rare, we can conclude that if it doesn’t cost
anything to store goods, the money rate of interest can’t be less than the expected
rise in prices. But many goods are even more expensive to store than apples, and
others can’t be stored at all (you can’t store haircuts, for example). For these goods,
the money interest rate can be less than the expected price rise.
How Well Does Fisher’s Theory Explain Interest Rates?
Not all economists would agree with Fisher that the real rate of interest is unaf-
fected by the inflation rate. For example, if changes in prices are associated with
changes in the level of industrial activity, then in inflationary conditions I might
want more or less than 105 apples in a year’s time to compensate me for the loss of
100 today.
We wish we could show you the past behavior of interest rates and expected in-
flation. Instead we have done the next best thing and plotted in Figure 24.2 the re-
turn on U.S. Treasury bills against actual inflation. Notice that between 1926 and
1981 the return on Treasury bills was below the inflation rate about as often as it
670 PART VII
Debt Financing
6
We oversimplify. If apples cost $1.00 apiece today and $1.10 next year, you need
next year to buy 105 apples. The money rate of interest is 15.5 percent, not 15. Remember, the exact for-
mula relating real and money rates is
where i is the expected inflation rate. Thus
In our example, the money rate should be
When we said the money rate should be 15 percent, we ignored the cross-product term i . This is
a common rule of thumb because the cross-product term is usually small. But there are countries where
i is large (sometimes 100 percent or more). In such cases it pays to use the full formula.
7
The apple example was taken from R. Roll, “Interest Rates on Monetary Assets and Commodity Price
Index Changes,” Journal of Finance 27 (May 1972), pp. 251–278.
8
There seems to be an exception to almost every statement. In late 1998 concern about the solvency of
some Japanese banks led to a large volume of yen deposits with Western banks. Some of these banks
charged their customers interest on these deposits; the nominal interest rate was negative.
1r
real
2
r
money
⫽ .05 ⫹ .10 ⫹ .101.052⫽ .155
r
money
⫽ r
real
⫹ i ⫹ i1r
real
2
1 ⫹ r
money
⫽ 11 ⫹ r
real
2 11 ⫹ i2
1.10 ⫻ 105 ⫽ $115.50