Core Inflation

Core inflation is a measure of the rate at which prices are rising that leaves out, or gives less weight to, items whose prices swing sharply for reasons unrelated to the general trend. The most common version removes food and energy from the consumer price index. The aim is to separate the persistent part of inflation from temporary noise, so that policymakers and analysts can judge where inflation is likely to settle.

It is contrasted with headline inflation, which covers the full basket of goods and services and reflects what households actually pay. Core inflation is not an alternative target; in most countries the official objective is defined in terms of the headline rate. Core measures are analytical tools used by central banks, finance ministries, investors and forecasters to interpret the headline figure.

There is no single definition. Statistical offices and central banks publish several measures, which fall into three groups:

• Exclusion measures. Specified categories are permanently removed. In the United States, core measures of the consumer price index (CPI) and of the personal consumption expenditures price index exclude food and energy. In the euro area, the standard core measure is the harmonised index excluding energy, food, alcohol and tobacco.
• Trimmed and median measures. Each month, the components with the largest and smallest price changes are discarded and the rest averaged, or the median change is taken. These exclude whatever happens to be extreme in a given month instead of a fixed list.
• Model-based and persistence-weighted measures. Components are weighted by how persistent or how sensitive to domestic economic conditions their prices have historically been, or a common trend is extracted statistically.

Food and energy prices are set largely in global commodity markets and are affected by weather, harvests, conflict and decisions of producers. They rise and fall sharply and often reverse. A jump in oil prices caused by a supply shock raises headline inflation immediately but may tell little about inflation a year or two ahead.

Monetary policy works with a delay, commonly estimated at a year or more, and it acts on demand in the economy. Raising interest rates cannot increase the supply of oil or grain. A central bank that reacted to every movement in commodity prices would tighten and loosen policy repeatedly, adding to instability in output and employment. Core inflation is intended to show the component of price pressure that reflects domestic demand, wages and expectations, which policy can influence.

Central banks that practise inflation targeting generally aim at a headline rate, typically 2%, over the medium term. They use core measures to judge whether a deviation from target is likely to persist. The Federal Reserve states its objective in terms of the overall personal consumption expenditures index but gives prominent attention to the core version in its projections and communications. The European Central Bank (ECB) targets headline harmonised inflation and monitors a range of underlying measures.

When headline inflation rises because of energy while core inflation stays stable, a central bank may choose to "look through" the increase and leave its policy interest rate unchanged. When core inflation itself rises, it suggests that price pressures have broadened, and a policy response is more likely. Core measures therefore feature heavily in forward guidance and in market expectations of rate decisions.

The distinction between headline and core is not permanent. A large or prolonged rise in energy or food prices raises firms' costs and reduces households' purchasing power. Firms pass costs on to other prices, and workers seek higher pay to compensate. If this continues, the initial shock spreads into core inflation and can feed a wage-price spiral. Whether it does depends greatly on whether the public expects inflation to return to target.

The episode that began in 2021 illustrated the process. Headline inflation in advanced economies rose sharply with energy, food and goods prices disrupted by the pandemic and the war in Ukraine. Core inflation followed with a lag, driven increasingly by services, and remained elevated after energy prices fell back.

The main objection is that core inflation leaves out things people must buy. Food and energy take a large share of the budgets of lower-income households, so a measure that omits them can seem remote from experience. The concept is defensible only as a guide to the trend, not as a measure of the cost of living.

There are technical objections as well. Excluded items are not always temporary: if energy or food prices rise faster than other prices for many years, a core measure will persistently understate inflation. Conversely, core measures retain volatile items of their own, such as airfares, used cars or housing costs, which can distort them. Different core measures can also give conflicting signals.

For these reasons, central banks present core inflation as one indicator among several, alongside wage growth, inflation expectations, measures of economic slack and upstream prices such as the producer price index (PPI). A combination of high inflation and weak growth is known as stagflation.