What Is the Consumer Price Index (CPI)?

7 min read

The Consumer Price Index tracks how the price of a representative basket of goods and services changes over time, making it the most commonly cited measure of inflation for the general public and financial markets alike.

Because so much of modern monetary policy is built around controlling inflation, CPI releases sit near the top of almost every trader's economic calendar.

How the basket is built

Statistical agencies construct the basket to reflect typical household spending - housing, food, transport, healthcare and more - and update its composition periodically so it continues to reflect real consumption patterns.

Because the weighting of each category is based on how households actually spend their money, changes in the basket over time can themselves shift how sensitive the index is to any one category's price swings.

• Basket weighting: Categories are weighted by their typical share of household spending.
• Periodic updates: Agencies revise the basket over time to reflect changing consumption habits.
• Regional variation: The exact basket and weighting differ from country to country.

Headline vs. core CPI

Headline CPI includes every category in the basket, while core CPI excludes food and energy prices, which tend to be more volatile month to month. Central banks often place more weight on core CPI as a cleaner read of the underlying inflation trend.

A gap between the two - for example, a headline figure pulled up sharply by an oil price spike while core inflation stays contained - is itself useful information about whether a price shock is likely to persist or fade.

• Headline CPI: The full basket, including volatile food and energy prices.
• Core CPI: Excludes food and energy for a steadier read on underlying inflation.
• Divergence signal: A wide gap between the two often points to a temporary, not structural, price shock.

Why CPI matters beyond economics textbooks

Because CPI feeds directly into central bank interest rate decisions, its release is one of the more reliably market-moving events on the calendar.

A CPI print that comes in meaningfully above or below consensus can shift interest rate expectations within minutes, which is why currency and bond markets in particular tend to react quickly and sharply to this specific release.

• Policy trigger: Persistent inflation surprises can directly change the expected path of interest rates.
• Bond market sensitivity: Yields often move immediately on a CPI surprise as rate expectations reprice.
• Currency impact: A currency can strengthen on hot inflation data if it raises the odds of tighter policy.