Overview

The consumer price index (CPI) is a statistical measure that summarizes how the prices of goods and services typically purchased by households change over time. It is widely used as a gauge of inflation and as a tool for comparing the purchasing power of money between periods. Because it reflects consumer outlays rather than production or export prices, CPI is central to everyday economic decisions.

How CPI is constructed

To calculate a CPI, statistical agencies select a "basket" of goods and services intended to represent typical household consumption. Prices for the items in the basket are collected regularly, and each item is assigned a weight that reflects its share of total consumer expenditure. Commonly used aggregation formulas combine price relatives into a single index whose movements indicate overall price change relative to a chosen base period.

Types and variants

  • Headline CPI includes the full basket, covering food, energy, housing, transportation, healthcare, and other categories.
  • Core CPI excludes volatile components such as food and energy to reveal underlying inflation trends.
  • Chained CPI and other chained indexes adjust weights over time to account for substitution between products when relative prices change.
  • Special indexes may be produced for different regions, urban vs. rural populations, or expenditure groups (for example, retirees).

Uses and importance

CPI is used to index wages, pensions, tax brackets, and social benefits so their real value is preserved. Central banks monitor CPI (and core measures) when setting monetary policy and inflation targets. Economists and businesses use CPI to deflate nominal series and compare real growth or to adjust contracts and budgets for expected price changes.

Limitations and criticisms

CPI does not perfectly measure changes in cost of living. Common issues include substitution bias (consumers switch to cheaper alternatives), difficulty measuring quality improvements, delayed inclusion of new goods, and differences in housing measurement across countries. Because of these issues, many agencies publish supplemental measures and methodological notes explaining revisions and seasonal adjustments.

Notable distinctions

CPI differs from other price measures such as the producer price index (which follows prices at earlier stages of production) and the GDP deflator (which covers all goods and services produced domestically). Understanding which index suits a particular purpose is important for policy, contracts, and research.