Nominal Interest Rates and Real Interest Rates

Mortgage rates and other interest rates are based on underlying dollar amounts; the interest rate tells you how many dollars borrowers must pay to lenders for each dollar that they borrow. Because they are based on dollar amounts, they are called nominal interest rates. When you see a mortgage rate quoted by a bank or a rate on a credit card, it is a nominal rate. The nominal rate does not tell us the true cost of borrowing, or return on lending, when there is inflation in an economy. For example, suppose that the nominal interest rate is 5 percent, but inflation is also 5 percent. If you took out a $1,000 loan, you would have to pay back $1,050 next year. But that $1,050 would buy exactly the same amount of real gross domestic product (real GDP) next year as $1,000 does this year—that is what it means to have 5 percent inflation. So, in terms of actual goods and services, you have to pay back the same amount that you borrowed. The real interest rate—that is, the interest rate corrected for inflation—is zero. Toolkit: Section 16.5 “Correcting for Inflation” The Fisher equation is a formula for converting from nominal interest rates to real interest rates, as follows: real interest rate ≈ nominal interest rate − inflation rate. The real interest rate gives the true cost of borrowing and lending; it is the real interest rate that actually matters for the decisions of savers and borrowers. [3] That doesn’t mean, by the way, that our previous two diagrams were incorrect because they used the nominal interest rate. Provided that the inflation rate doesn’t change, a comparative static exercise using the nominal interest rate will give you exactly the same conclusion as one using the real interest rate. Individual Credit Markets and the Aggregate Credit Market We have described a market for a particular kind of loan, but more generally we know that there are all kinds of different ways in which credit is offered in an economy. Households borrow from banks to buy houses or cars. Households and firms make purchases using credit cards. Firms borrow from financial institutions to buy new equipment. The government borrows to finance its spending, and so on. There is a very large number of credit markets in the economy, each offering a different kind of credit, and each with its own equilibrium interest rate. These different credit markets are linked because most households and firms buy or sell in more than one market. Financial institutions in particular trade in large numbers of different credit markets. For much of what we do in macroeconomics, however, the distinctions among different kinds of credit are not critical, and it is sufficient to imagine a single aggregate credit market and a single real interest rate.