The full U.S. CPI report.

The CPI-U — the Consumer Price Index for All Urban Consumers — is the index almost every headline refers to. It covers urban consumers, who make up roughly 93 percent of the U.S. population, and it is the basis for the inflation rate reported in the press, for Treasury Inflation-Protected Securities, and for most private-sector cost-of-living adjustments.

The CPI-W — the Consumer Price Index for Urban Wage Earners and Clerical Workers — covers a narrower group: about 29 percent of the population, restricted to households where a majority of income comes from clerical or hourly wage occupations. CPI-W is the index the Social Security Administration uses to calculate the annual cost-of-living adjustment (COLA) for retirement, survivor, and disability benefits. The SSA compares the third-quarter average of CPI-W against the same quarter a year earlier; the percent change, rounded to the nearest tenth, becomes the next year's COLA.

The C-CPI-U, or Chained CPI for All Urban Consumers, was introduced in 2002 to address a long-running criticism of CPI: that it doesn't capture how consumers substitute toward cheaper alternatives when prices change. The chained formula uses an updated expenditure-weighted geometric mean across categories and tends to grow slightly more slowly than CPI-U — by roughly a quarter of a percentage point per year on average. Since the 2017 Tax Cuts and Jobs Act, C-CPI-U has been the index used to adjust federal income tax brackets, the standard deduction, and many other Internal Revenue Code parameters.

One more useful distinction: seasonally adjusted versus not seasonally adjusted. The headline month-over-month figures you see in news coverage are seasonally adjusted, removing predictable patterns like winter heating costs or back-to-school clothing demand. The 12-month year-over-year change is typically reported on the not-seasonally-adjusted index, since the seasonal effects wash out over a full year. Only the seasonally adjusted series gets revised — once a year, every February, when five years of seasonal factors are updated.

One of the structural features that makes CPI useful for legal contracts and benefit calculations is that the not-seasonally-adjusted index is never revised after publication. Once a month's CPI prints, that number is locked in. Social Security recipients, lease tenants tied to CPI escalators, and TIPS bondholders can rely on the figure they were paid out on.

The seasonally adjusted figures are different. Each February, BLS releases updated seasonal factors covering the prior five years. This means month-over-month seasonally adjusted readings from the last several years can shift slightly. The annual updates are small in any given month but occasionally rewrite the narrative around a turning point — for example, what looked like a clear inflation peak in real time can later be revised to a different month, or made less or more dramatic.

Larger structural changes happen less often. BLS updates the CPI expenditure weights annually now, but for decades did so only every two years. The basket itself — the specific items priced — is refreshed continually through item rotation, and the geographic sampling has been updated periodically as well. The 1998 introduction of the geometric-mean formula at the lower level of aggregation, the introduction of hedonic quality adjustments for tech goods, and the shift to annual weight updates in 2023 are the most consequential methodology revisions of the past quarter century.

What to watch in the next print

For any upcoming CPI release, three numbers usually matter most. First, the headline year-over-year change, because that's the figure that drives news coverage and political reaction. Second, the core month-over-month change, because the Fed pays closest attention to underlying momentum stripped of food and energy noise. Third, shelter, because at ~35% of the basket it can single-handedly determine whether the headline disinflates or stalls. Within shelter, watch the spread between owners' equivalent rent (OER) and the rent of primary residence — they normally move together, and a sudden gap is often a methodology artifact rather than a real-economy signal.

Beyond those three, market participants increasingly track "supercore" services — core services excluding shelter — because it's a closer proxy for wage-driven inflation that the Fed believes it can influence with rate policy. A persistent supercore reading above 4% annualized tends to keep the Federal Reserve hawkish even when headline CPI is cooling. For deeper coverage, see our core CPI page and the CPI vs PPI comparison.