The Consumer Price Index (CPI) measures the average change over time in the prices paid by urban consumers for a basket of goods and services. Published monthly by the Bureau of Labor Statistics (BLS), it is the most widely followed measure of inflation in the United States.
Why It Matters
CPI directly affects the daily lives of every American. It determines cost-of-living adjustments for Social Security recipients, influences wage negotiations, and guides rental agreements with escalation clauses. For investors and policymakers, CPI is the primary gauge of whether prices are rising too quickly (inflation) or falling (deflation).
The CPI Basket
The BLS surveys approximately 80,000 consumer items across 75 urban areas monthly. The basket is weighted by typical consumer spending patterns:
CPI vs. Core CPI
Headline CPI includes all items. Core CPI excludes food and energy prices, which tend to be volatile. The Federal Reserve pays more attention to Core CPI (and PCE) for policy decisions because it gives a clearer picture of the underlying trend. Analysts increasingly watch "supercore" inflation—core services excluding shelter—as the cleanest read on demand-driven price pressure.
The Shelter Lag
Shelter is roughly a third of the basket, and the BLS measures it largely through Owners' Equivalent Rent (OER). Because leases reset slowly, this component trails real-time market rents by 6–12 months—so CPI can keep showing elevated housing inflation long after spot rents have cooled, a frequent source of confusion when reading the data.
CPI-U, CPI-W and Chained CPI
The headline number is CPI-U, covering urban consumers (~93% of the U.S. population). A separate CPI-W (urban wage earners) sets annual Social Security cost-of-living adjustments, while the Chained CPI (C-CPI-U) accounts for consumer substitution and rises more slowly—which is why it is used to index federal tax brackets.
Year-over-Year Measurement
The CPI growth rate shown on ECONPLEX represents the year-over-year percentage change, comparing the current month's index level to the same month one year ago. This approach smooths out seasonal variations.
Market Impact
A hotter-than-expected CPI print often triggers sell-offs in both bonds and stocks, strengthens the dollar, and increases the probability of Fed rate hikes. A cooler reading has the opposite effect—boosting bonds and risk assets while weakening the dollar. Released around the second week of each month at 8:30 a.m. ET, CPI is one of the single most market-moving data points: U.S. headline CPI peaked at 9.1% year-over-year in June 2022—a roughly 40-year high—before decelerating sharply.