Overview

An interest rate is the charge imposed by a lender on a borrower for the use of money, usually expressed as a percentage of the principal over a period of time. For a simple example, a 10% annual interest rate on a $100 loan requires $110 to be repaid after one year. Rates can be quoted in many ways and influence decisions by households, businesses and governments.

Key characteristics and types

Interest rates come in several forms and are described by different terms:

  • Nominal rate: the stated percentage without adjustment for inflation. See percentage conventions for common quotations.
  • Real rate: the nominal rate minus inflation, showing the true purchasing‑power return.
  • Simple vs compound: simple interest applies only to principal; compound interest accrues on interest already earned.
  • Fixed vs variable: fixed rates stay unchanged for a period; variable (or floating) rates move with market benchmarks.

How rates are set

Central banks influence short-term interest rates through policy decisions and a base or policy rate; commercial rates available to consumers and firms are typically set above that base. For background on central-bank roles, see central bank guidance. Lenders also add risk premia to reflect credit risk, term length and liquidity.

Historical context

Charging for the use of money has ancient roots in lending practices and trade. Societies have long debated and regulated excessive charges—historically called usury. The modern system of market interest rates developed alongside banking, government debt markets and central banking from the early modern period onward.

Economic importance and examples

Interest rates affect mortgage costs, business investment decisions, bond yields and savings returns. They are a key tool of monetary policy: raising rates tends to cool inflation and slow demand, while cutting rates can stimulate borrowing and spending. The relationship between nominal rates, inflation and expectations is summarized by the equation real rate ≈ nominal rate − inflation.

Notable distinctions and recent phenomena

  1. Negative nominal rates have appeared in some economies, implying lenders pay to hold certain assets.
  2. Yield curves plot rates across maturities and signal market views of future growth and inflation.
  3. Interest spreads compensate lenders for credit and liquidity risk.

For concise definitions and guides to common rate measures and acronyms, search introductory resources on interest and policy rate mechanics.