September delivered two different inflation stories at once. Headline consumer prices rose 3.7% from a year earlier. Strip out food and energy, and the same economy’s inflation rate was 2.6%. The Federal Reserve’s preferred gauge told yet another version: 3.6% headline, 3.1% core.
The gap between those numbers is the whole point of core inflation. It is the single most cited — and most misunderstood — concept in the inflation debate, and right now it sits at the centre of the Fed’s December decision. This explainer covers what core inflation measures, why two different “core” numbers can disagree by half a point, and what the September data actually says about underlying price pressure.
What Core Inflation Is
Core inflation is simply a price index with food and energy removed. The most quoted version, core CPI, is the Consumer Price Index for All Urban Consumers “less food and energy.” Its PCE cousin, core PCE, applies the same exclusion to the Personal Consumption Expenditures price index.
The exclusion exists for one reason: volatility. Food and energy prices swing on forces that have little to do with the domestic demand the Fed is trying to manage — wars, weather, OPEC decisions, harvests. September 2026 is a textbook case. Gasoline jumped 9.1% in a single month, accounting for more than half of the entire monthly rise in headline CPI, according to the Bureau of Labor Statistics. Over the year, gasoline is up 34.2% and the whole energy index 20.4%. Food, by contrast, was flat on the month and up 2.5% on the year.
A central bank that reacted to every oil spike would be tightening into a war one month and easing into a harvest the next. Core inflation is an attempt to look through that noise and see whether price pressure is broad-based and persistent — the kind that tends to feed into wages and expectations, and the kind that interest rates can actually influence.
The September 2026 Scorecard
The latest readings, from the two official releases, tell a consistent story: inflation is above target on every measure, and the “core” measures are firmer than the headline numbers suggest about the underlying trend.
| Measure | Monthly change | Annual rate | August annual rate |
|---|---|---|---|
| Headline CPI | +0.6% | 3.7% | 3.4% |
| Core CPI | +0.3% | 2.6% | 2.4% |
| Headline PCE | +0.5% | 3.6% | 3.4% |
| Core PCE | +0.3% | 3.1% | 3.0% |
Three readings of our own from these numbers are worth more than the headlines alone.
First, the wedge. Headline CPI exceeds core CPI by 1.1 percentage points (3.7% versus 2.6%) — almost entirely an energy story, with the energy index up 20.4% over the year. When the gap is this wide, the headline number is mostly telling you about oil, not about the economy.
Second, the momentum. Core CPI has now risen 0.3% in two consecutive months, after 0.2% in July. Add the three months together — 0.8% — and annualise it, and the recent pace of core inflation is about 3.2% a year, noticeably above the 2.6% year-on-year rate. The year-on-year figure looks backwards; the three-month pace looks at where prices are heading right now. On that measure, underlying inflation is firming, not cooling: the annual core rate rose from 2.4% in August to 2.6% in September.
Third, the core-versus-core gap. Core PCE, the Fed’s preferred gauge, runs 0.5 points above core CPI (3.1% versus 2.6%). Both measures rose 0.3% on the month, so the difference is not about September — it is about how the two indexes are built.
Core CPI vs Core PCE: Why Two “Cores” Disagree
If both measures exclude the same two categories, why do they give different answers? Three design differences explain most of it.
Weights. Shelter is the largest single component of the CPI basket, and it rose 3.2% over the year to September. Housing carries a much smaller weight in the PCE index, and it is measured differently there. When rents are the main source of stickiness, CPI feels it more; when other services are the story, PCE can run hotter, as it does now.
Scope. CPI tracks what urban consumers pay out of pocket. PCE tracks all consumption spending, including spending made on households’ behalf — employer-paid health insurance, and government-funded medical care such as Medicare and Medicaid — plus spending by non-profit institutions. That broader basket responds differently to price changes in healthcare and services.
Formula. CPI is built on a fixed basket of goods that is updated periodically, while PCE is a chain-type index that lets the basket evolve as consumers substitute cheaper alternatives. Substitution usually pulls PCE below CPI over time — but not always, and not in every category. The result is that the two gauges rarely agree to the decimal point, and the gap itself moves around.
The practical consequence for readers: when commentators cite “core inflation” without saying which one, they may be talking about numbers half a point apart. Our comparison of CPI vs PCE inflation goes deeper into the two indexes’ construction.
Why the Fed Watches Core
The Fed’s 2% inflation target is defined in terms of headline PCE inflation, not core. But officials watch core closely for three reasons.
First, core is a better predictor of where headline is heading. Energy shocks fade — gasoline that surges 34% in a year rarely repeats the trick — while broad-based services inflation tends to persist. A core rate stuck above 3% tells policymakers that even if oil calms down, inflation is unlikely to return to 2% on its own.
Second, monetary policy works with long lags. Rate changes take many months to filter through borrowing, hiring and spending. Policymakers cannot steer by a number that whipsaws with each oil shock; they need a steadier signal to aim at. Core provides it, imperfectly.
Third, core maps more directly onto the domestic economy the Fed can influence. Oil prices are set in world markets. Rents, wages, restaurant meals and insurance premiums are set at home — and those are the prices that show up in the core basket.
That is why September’s data complicated the Fed’s job. The central bank held its benchmark rate at 3.75%–4.00% on October 28, with two officials dissenting in favour of a hike. Core PCE at 3.1%, up from 3.0% in August, gives the hawks their argument: underlying inflation is not just above target, it is edging the wrong way. The doves’ counter is that the three-month core CPI pace of about 3.2% annualised is still well below the pace of a year ago, and that restrictive policy needs time to work. The next decision comes on December 9, when the Fed also publishes updated economic projections. For the mechanics of how the Fed turns data like this into a rate decision, see our guide to how the Fed sets interest rates.
What Core Inflation Misses
Core is a filter, not a fact. Used carelessly, it misleads in at least four ways.
Households do not eat “core.” Food and energy are excluded for analytical reasons, but they are real costs. A 34% annual rise in gasoline hits household budgets whether or not it appears in the core index. When core and lived experience diverge, public trust in the official numbers erodes — a cost the Fed is aware of.
Shelter lags. Rents in the CPI reflect leases signed months ago, so shelter inflation is slow to turn in either direction. A 3.2% annual shelter reading today partly describes the rental market of last spring.
It can miss persistent supply shocks. Stripping out food and energy assumes their price moves are temporary. When a shock persists — as energy did through much of 2022 — core understates the inflation households actually face, and can understate the second-round effects as higher transport and production costs seep into everything else.
It is not the only filter. The Fed also watches trimmed-mean and median measures — the Dallas Fed’s trimmed-mean PCE and the Cleveland Fed’s median CPI — which strip out the most extreme price moves in either direction each month rather than always excluding the same two categories. Those alternatives are a useful cross-check when core and headline tell very different stories, as they do now.
What to Watch Next
| Date | Release | Why it matters |
|---|---|---|
| Nov 10, 8:30 a.m. ET | October CPI | First read on whether core CPI holds its 0.3% monthly pace — and whether the energy-driven headline gap narrows |
| Nov 25, 8:30 a.m. ET | October PCE | Core PCE check ahead of December; released alongside the second estimate of third-quarter GDP |
| Dec 8–9 | FOMC meeting | Rate decision on Dec 9 at 2:00 p.m. ET, plus updated economic projections |
The question for all three dates is the same one September posed: is underlying inflation settling, or is it re-accelerating? Core PCE has now spent months above 3%, and the three-month core CPI pace is running hotter than the annual rate. If October’s data confirms that pattern, the case for another hike in December strengthens. If core softens back toward 0.2% a month, the wait-and-see camp gains ground. Our Federal Reserve meeting schedule for 2026 lays out the dates and what to watch at each one.
Frequently Asked Questions
Is core inflation the same as “underlying inflation”?
Roughly, but not exactly. “Underlying inflation” is a concept — the persistent, broad-based component of price growth. Core inflation is one practical estimate of it, obtained by removing food and energy. Trimmed-mean and median measures are other estimates. They usually agree on direction but often differ on the level.
If food and energy are excluded, why does the Fed care about gas prices?
Because energy costs feed into everything else. Higher fuel prices raise transport and production costs, which eventually appear in the prices of goods and services that are in the core basket. The Fed watches energy directly for those second-round effects and for what it does to inflation expectations — even though energy itself is not in the core index.
Does the Fed target core PCE?
No. The Fed’s 2% target is defined for headline PCE inflation — the full index, food and energy included. Core PCE is a guide to where headline is likely to go, not the target itself. In the long run, the distinction should not matter: if core stays above 2%, headline cannot stay at 2% either.
Macrometer is an independent macroeconomics publication. This article is for informational purposes only and is not financial advice. Inflation figures are subject to revision by the Bureau of Labor Statistics and the Bureau of Economic Analysis.
