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What the Consumer Price Index is
The Consumer Price Index measures the average change over time in the prices that households pay for a basket of goods and services. The percentage change in CPI from one year to the next is the most common headline figure for inflation.
In other words, CPI is the yardstick. When you hear that inflation is running at a certain rate, that figure usually comes from the change in this index. Our guide on inflation explains the broader concept that CPI is built to measure.
How it is built
Statisticians define a representative basket of what a typical household buys, covering things like food, housing, transport, medical care, and recreation. Each category is weighted by how much people actually spend on it, so housing counts for more than, say, postage.
Prices for the items in the basket are collected regularly, and the index tracks how the cost of that whole basket changes. The result is a single number that summarizes the cost of living.
Headline vs core CPI
Headline CPI includes everything in the basket, including food and energy, whose prices can swing sharply month to month. Core CPI strips out food and energy to reveal the steadier underlying trend.
Both matter. Headline CPI reflects what people actually feel at the store and the pump, while core CPI is often what central banks focus on when judging where inflation is really heading.
💡 Core filters out the noise:Food and energy prices are volatile, so a single month of headline CPI can be misleading. Core CPI removes them to show the more persistent trend that policymakers care about.
Why markets react to it
CPI is one of the most market-moving releases because it shapes expectations for interest rates. Higher-than-expected inflation can push a central bank toward raising rates, while cooler readings can do the opposite, and both ripple through stocks, bonds, and currencies.
Because so much rides on it, even a small surprise in the monthly figure can trigger sharp moves across markets.
Its limits
A single national index cannot match everyone's experience. Your personal inflation rate depends on what you actually buy, so a retiree, a student, and a family can all feel inflation differently from the headline figure.
The basket and methods also evolve over time, and people change their habits as prices shift, which makes any single measure of the cost of living an approximation rather than a perfect gauge.
Frequently asked questions
What is the Consumer Price Index?
The Consumer Price Index, or CPI, measures the average change over time in the prices households pay for a basket of goods and services. The yearly change in CPI is the most common headline measure of inflation.
What is the difference between headline and core CPI?
Headline CPI includes all items, including volatile food and energy prices. Core CPI excludes food and energy to show the steadier underlying trend. Central banks often focus on core to judge where inflation is really heading.
How is CPI used to measure inflation?
Inflation is usually reported as the percentage change in CPI over the past year. Because CPI tracks the cost of a representative basket of goods and services, its rate of change is treated as the headline inflation rate.
Why do markets react so strongly to CPI?
CPI heavily influences expectations for interest rates. A hotter reading can push a central bank toward raising rates and a cooler one toward easing, so even small surprises can move stocks, bonds, and currencies sharply.
Related tools and pages
These are for learning. Any calculator here shows example scenarios, not predictions of future prices.
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