What each measure includes
Headline CPI covers the full consumer basket: food, energy, shelter, vehicles, medical care, and everything else the Bureau of Labor Statistics tracks. Core CPI is the same basket minus food and energy — roughly a fifth of the total by weight.
Excluding food and energy is not a claim that they don't matter to households. It is a statistical choice: those two categories are dominated by global commodity markets and weather, so they inject volatility that can mask what domestic prices are doing underneath.
Why the two diverge
When oil prices spike or crop failures push food costs up, headline inflation jumps while core moves little — 2022's peak headline readings owed several percentage points to energy alone. The reverse happens when commodities fall: headline can drop below core, as it did through much of 2023 while shelter costs kept core elevated.
Historically, large gaps between the two have tended to close from the headline side: commodity shocks fade, and headline converges back toward core. That is why economists treat core as the better read on where inflation is settling, and the gap itself as a rough gauge of how much of current inflation is commodity noise.
Which one the Fed watches
The Federal Reserve's stated 2% target is in headline PCE terms, but its communications and forecasts consistently emphasize core measures when judging progress. Policymakers reason that monetary policy cannot grow more wheat or pump more oil — it acts on the demand-driven part of inflation that core isolates.
Markets follow the same convention: core CPI and core PCE releases typically move rates and equities more than the headline figure when the two tell different stories.
How to read the gap
Headline above core has historically signaled a commodity-driven episode — uncomfortable for households, but the kind of inflation that has tended to pass without policy tightening if expectations stay anchored. Core above headline has been the more stubborn configuration, since the categories driving it (shelter, services, wages) reprice slowly.
The breakeven inflation rate, charted below, shows what bond markets expect inflation to average over the next decade — a useful third reference when core and headline disagree.