The Consumer Price Index measures the average change in prices urban consumers pay for a fixed market basket of goods and services, calculated monthly by the Bureau of Labor Statistics from roughly 94,000 price quotes collected in person, by phone, and from retail scanner and web data. The July 2025 reading showed prices up 2.7 percent from a year earlier, per the BLS release of August 12, 2025. The index is the benchmark for cost-of-living adjustments to Social Security, union contracts, and tax brackets. The Daily News 24 publishes information, not investment advice.
What the number measures, and what it does not, is set entirely by published methodology — the basket, the weights, and the arithmetic. Each is auditable in the BLS handbook, and each carries a documented limit.
Where do the prices come from?
BLS economic assistants sample prices for some 200 categories of items across 32 urban areas, supplementing field collection with retail transaction data — scanner feeds and web-scraped prices now supply a large share of quotes, per the BLS handbook of methods. Categories range from cereals to hospital services, and each item is priced the same way each month so the index measures change, not level. A price that rises while quality also rises gets a quality adjustment; a laptop with twice the memory is not pure inflation.
How are the items weighted?
By spending shares from the Consumer Expenditure Survey, in which roughly 20,000 households per two-week wave log what they buy. Shelter holds the largest share at about 35 percent of the index; food about 13 percent; energy about 6 percent. The weights update on a two-year cycle, which means a category whose share changes fast — used cars in 2021, for example — influences the index with a lag.
The weighting is where the index's known blind spots live. The CPI covers urban consumers only, is indexed to a fixed basket that adjusts for substitution slowly, and treats homeowners' costs through owners' equivalent rent rather than house prices. Each choice is documented in the methodology; none is hidden.
Why does shelter move so slowly?
Because the rent component averages all tenants' rents, not just new leases. Existing tenants' rents change mostly at renewal, so market rent moves reach the index over roughly a year. In the 2021-22 rent surge the CPI shelter component kept accelerating into 2023 after market-rate asking rents had flattened — a lag the BLS publishes and forecasters track. Shelter's 35 percent weight means this single lag dominated core CPI for two years.
What is the CPI used for?
Three anchors sit on the number:
- Cost-of-living adjustments: Social Security's annual COLA is computed from CPI-W, a variant index, by formula in statute.
- Contracts and indexation: rents, alimony, and union wage scales tie escalators to published CPI series.
- Policy and markets: the Federal Reserve's inflation target uses PCE, but CPI drives the market's first monthly read, and Treasury inflation-protected securities principal is indexed to CPI itself.
What does the index not measure?
Anyone's actual basket. A household that drives 100 miles a week or spends 15 percent of income on food experiences a different inflation rate than any aggregate; the BLS publishes an experimental calculator acknowledging exactly this. The index is an average of urban spending, weighted by dollars — and dollars are spent unevenly.
What the methodology establishes is a number built to be reproducible. What it cannot establish is the rate any one household faces; the basket is the statistic's, not the shopper's.
For more context, read Retail Sales Fall 0.6% in July as Inflation Holds at 3.4%.