Lably
Skip to content

Interest rate

Percentage of a sum of money charged for its use

  • 15 min read
  • 4 chapters
  • 2 labs on Lably

Learn it on Lably

Interest rates reflect a borrower's willingness to pay for money now over money in the future. In debt financing, companies borrow capital from a bank, in the expectation that the borrowed capital may be used to generate a return on investment greater than the interest rates. Failure of a borrower to continue paying interest is an example of default, which may be followed by bankruptcy proceedings. Collateral is sometimes given in the event of default.

In monetary policy and macroeconomics, the term "interest rate" is often used as shorthand for a central bank's policy rate, such as the United States Federal Reserve's federal funds rate. "Interest rate" is also sometimes used synonymously with overnight rate, bank rate, base rate, discount rate, coupon rate, repo rate, prime rate, yield to maturity, and internal rate of return.

Definitions

Real versus nominal

The nominal interest rate is the interest rate without adjusting for inflation, whereas the real interest rate takes inflation into account. Real interest rates measure the interest accumulated and repayment of principal in real terms by comparing the sum against the buying power of the amount at the time it was borrowed, lent, deposited or invested. Where inflation is the same as nominal interest rate, the real interest rate is zero.

The real interest rate is given by the Fisher equation:

r=1+i1+p−1

where p is the inflation rate.

For low rates and short periods, the linear approximation applies:

r≈i−p

The Fisher equation applies both ex ante and ex post. Ex ante, the rates are projected rates, whereas ex post, the rates are historical.

Other rates

The term "interest rate" is also often used as shorthand for a number of specific rates, most commonly the overnight rate, bank rate, or other interest rate set by a central bank. In this regard, the United States Federal Reserve's Federal Funds Rate is often simply known as the "interest rate" or "rate", due to its global macroeconomic and financial significance. In United Kingdom contexts, Official Bank Rate of the Bank of England is also known as "the interest rate". "Interest rate" is also sometimes used synonymously with base rate, discount rate, coupon rate, repo rate, prime rate, yield to maturity, internal rate of return, spot rate, forward rate, and benchmark rates such as Libor and SONIA.

Base rate usually refers to the annualized effective interest rate offered on overnight deposits by the central bank or other monetary authority.

The annual percentage rate (APR) may refer either to a nominal APR or an effective APR (EAPR). The difference between the two is that the EAPR accounts for fees and compounding, while the nominal APR does not.

The annual equivalent rate (AER), also called the effective annual rate, factors into account compounding frequencies of products, but does not account for fees.

Discount rate can both refer to the discount window of central banks and more generally as the annual rate used to discount future values into present value.

A bond's coupon rate is its interest rate, while its current yield is the ratio of its annual interest payment to its current market price.

Yield to maturity is a bond's expected internal rate of return, assuming it will be held to maturity, that is, the discount rate which equates all remaining cash flows to the investor (all remaining coupons and repayment of the par value at maturity) with the current market price.

Based on the relationship between supply and demand of market interest rate, there are fixed interest rate and floating interest rate.

Sign in to keep reading

3 more chapters are free with a Lably account.

More in Politics and economics