What is CPI (Consumer Price Index)? A Simple Guide

The Consumer Price Index, or CPI, tracks the average change in prices of a basket of goods and services that households buy. It is the main measure of retail inflation. A rising CPI means the cost of living is going up. Central banks watch it closely when setting interest rates.

To measure inflation, you need to track prices of the things people actually buy. The Consumer Price Index does exactly that, following a basket of everyday goods and services.

This guide explains how CPI works and why it is the headline inflation measure.

Key Takeaways

• CPI tracks prices of a household basket of goods and services.
• It is the main measure of retail inflation.
• A rising CPI means a higher cost of living.
• Central banks watch it to set interest rates.
• The basket is weighted by spending patterns.

What does CPI measure?

CPI measures the average change in the prices of a fixed basket of goods and services that a typical household consumes, such as food, housing, transport and clothing. By tracking how the cost of this basket changes, CPI captures the inflation that ordinary people actually experience at the shop.

How is CPI used?

CPI is the headline measure of retail inflation, quoted when inflation is reported. Central banks use it to judge whether inflation is within their target, guiding interest rate decisions. It is also used to adjust wages, pensions and contracts for the rising cost of living in many cases.

How is the basket weighted?

Not everything is bought equally, so items in the basket are weighted by how much households spend on them. Food and housing usually carry large weights, while minor items carry small ones. This means a price rise in a heavily weighted item, like food, moves the CPI more than the same rise in a minor item.

Why does CPI matter to markets?

CPI drives expectations about interest rates. A higher-than-expected CPI can prompt fears of rate hikes, which weigh on stocks and bonds, while a softer reading can lift them. Because it shapes central bank policy, a single CPI release can move markets sharply on the day it is published.

How is CPI different from WPI?

CPI measures prices at the retail level, what consumers pay, while the wholesale price index measures prices at the producer or wholesale level, before goods reach the shop shelf. CPI also includes services and reflects distribution costs and taxes, which the wholesale index generally does not. The two can diverge, sometimes sharply, and when they differ it can signal that cost pressures are building or easing along the supply chain before they fully reach households.

What is core CPI?

Headline CPI includes everything, food and fuel included, which can be very volatile. Core CPI strips out these volatile items to reveal the underlying trend in prices. Policymakers watch both: headline shows what households actually feel in their daily spending, while core shows the more persistent inflation that policy needs to address. A gap between the two often points to a temporary food or fuel shock rather than a lasting change in the inflation trend.

Economic data, policy and rates change over time and affect markets in complex ways. This article is educational, uses figures for illustration only, and does not constitute investment advice.

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