Inflation Explained

Inflation is the slow erosion of purchasing power — and CPI, Core CPI, PPI, and PCE are four different rulers economists use to measure it.

What inflation measures

Inflation is the rate at which prices for goods and services rise over time, meaning each dollar buys a little less than it used to. A mild, steady inflation rate is normal in a growing economy — wages tend to rise alongside prices, and businesses can plan around predictable costs. Problems start when inflation accelerates faster than incomes or swings unpredictably, because that uncertainty makes it harder for households to budget and for companies to set wages and plan investment.

Markets don't experience inflation directly. They experience the reports that measure it. That's why traders spend so much energy parsing the difference between CPI, Core CPI, PPI, and PCE — four indices that all describe inflation but capture different slices of the economy and get built in different ways.

CPI and Core CPI: what shoppers pay

The Consumer Price Index tracks the price of a fixed basket of goods and services that a typical household buys — rent, groceries, gasoline, medical care. It's the most widely cited inflation number because it maps directly onto what people actually spend money on.

Core CPI strips out food and energy prices, which swing sharply for reasons that have little to do with underlying economic conditions — a drought, a pipeline outage, a geopolitical shock. Removing that noise gives a cleaner read on the trend that's more likely to persist, which is why policymakers weight it heavily when deciding on interest rates.

PPI: inflation from the producer's side

The Producer Price Index measures the prices businesses receive for what they sell, before those costs reach the end consumer. Because producer costs often show up in consumer prices with a lag, PPI is sometimes read as a leading indicator — a rise in what factories charge wholesalers today can hint at what shoppers might pay in a few months.

PCE: the Fed's preferred gauge

The Personal Consumption Expenditures index is broader than CPI and adjusts its basket more frequently to reflect how consumers substitute one good for another as prices shift — buying chicken instead of beef, say, when beef gets expensive. The Federal Reserve names Core PCE its preferred inflation gauge partly because that substitution effect makes it a more accurate reflection of real-world spending behavior.

None of these four numbers is the truth about inflation. Each is a different lens, and markets watch all of them because a gap between what CPI says and what PCE says can shift expectations for how the Fed will act.