How Inflation Actually Works — and Why Markets Obsess Over It

Inflation is the most quoted and least understood number in economics. Headlines announce it monthly, central banks stake their credibility on it, and entire market selloffs have followed a reading that came in a tenth of a percent above expectations. What is actually being measured — and why does it move trillions of dollars?

What inflation is

Inflation is a sustained rise in the general level of prices, which is the same thing as a sustained fall in the purchasing power of money. The key word is general: one product getting expensive is not inflation. Everything getting expensive, on average, is.

It is measured with price indices. The two you will see most in the United States:

• CPI (Consumer Price Index): published monthly by the Bureau of Labor Statistics. It tracks a basket of goods and services urban consumers buy — housing, food, transport, healthcare, and more.
• PCE (Personal Consumption Expenditures price index): published by the Bureau of Economic Analysis. It covers a broader basket, including some spending done on consumers’ behalf (such as employer-paid healthcare), and its formula adapts more quickly as shoppers substitute cheaper alternatives.

Economists usually quote the year-over-year change: prices today versus the same month last year. A 3% reading means the basket costs 3% more than it did twelve months ago.

Why the Fed watches PCE, but markets jump on CPI

The Federal Reserve’s official target is 2% annual inflation as measured by PCE, a goal it formalized in 2012. The Fed prefers PCE because its chain-weighted construction reflects how Americans actually shift their spending — if beef gets expensive and shoppers switch to chicken, PCE captures that substitution faster than CPI’s more fixed basket. PCE also typically runs a few tenths of a point lower than CPI over long stretches.

Yet CPI routinely triggers the bigger immediate market reaction. It is released earlier each month, giving investors their first major read on consumer price pressures, while PCE arrives weeks later. Traders react to CPI because it is the earliest signal; the Fed sets policy off PCE because it is the better measure. Knowing which number matters to whom explains a lot of apparently contradictory market behavior.

Inside the CPI basket: the housing quirk

Here is something most headlines skip: shelter — housing costs — makes up roughly 35 to 36 percent of the CPI, the single largest component by far. Within that, “owners’ equivalent rent” (about 26% of the index) estimates what homeowners would pay to rent their own homes, imputed from actual rental data the BLS collects from roughly 40,000 residences. House prices themselves are deliberately excluded: the BLS treats a home as part investment, part consumption, and the index aims to capture only the shelter service it provides.

This creates two quirks worth knowing. First, CPI shelter lags real-world rents by many months, because leases turn over slowly and the survey samples each unit only twice a year. Second, when mortgage rates spike, CPI barely notices — mortgage interest is classified as a capital cost, not consumption. Anyone who felt housing pain in 2022–2023 while watching CPI shelter creep upward months late has lived this lag firsthand.

Analysts also split the index into headline (everything, including volatile food and energy) and core (excluding food and energy). Core is the steadier signal of underlying pressure — the number central bankers cite when they say they are “looking through” a gasoline spike.

Where inflation comes from

Textbooks divide causes into buckets, and reality usually mixes them:

Demand-pull. Too much spending chasing too few goods. When economies reopened after pandemic lockdowns, stimulus-swollen demand collided with constrained supply chains, and prices surged. Classic demand-pull.

Cost-push. Input costs rise and businesses pass them on. An oil shock raises transport and manufacturing costs across the economy; wages rising faster than productivity do the same.

Expectations. The subtlest channel. If businesses expect 5% inflation, they raise prices preemptively; workers demand matching raises. The expectation fulfills itself. This is why central bankers obsess over “anchoring expectations” — credibility is itself a policy tool.

Money supply (the long-run view). Over long horizons, inflation tracks how fast the money supply grows relative to real output. Short-run noise aside, you cannot print purchasing power.

A case study: the 2021–2022 surge

The mechanics above stopped being theoretical in 2021. U.S. CPI inflation climbed through that year and peaked at 9.1% year-over-year in June 2022 — the largest 12-month increase since 1981, according to the BLS. Energy prices had risen more than 40% over the year, food prices by double digits, and shelter was accelerating.

The episode was a pile-up of nearly every cause at once: pandemic stimulus juicing demand, snarled supply chains and chip shortages constraining supply, Russia’s invasion of Ukraine spiking energy and grain prices, and a tight labor market pushing wages up. The Fed, which had initially described the rise as “transitory,” pivoted to the fastest rate-hiking cycle in decades. Markets that had priced in calm were forced to reprice everything — which is precisely why inflation prints move asset prices so violently.

Why markets hang on every inflation print

1. It sets the path of interest rates. Central banks raise rates to fight inflation and cut them to support growth. An inflation surprise reprices the entire expected path of rates — and interest rates are the gravity of finance: they discount every future cash flow. Our explainer on bond yields traces this transmission in detail.

2. It hits bonds first, stocks second. Inflation erodes the real value of fixed payments, so bond prices fall and yields rise when inflation surprises upward. Stocks suffer through higher discount rates and squeezed margins — though companies with pricing power can pass costs through.

3. It redistributes wealth silently. Inflation transfers purchasing power from lenders to borrowers and from cash-holders to asset-owners. A fixed-rate mortgage becomes cheaper in real terms when inflation runs hot. Capital also chases the currencies of countries with credible low inflation, which is why CPI surprises move exchange rates.

This transmission — data to rates to asset prices — is the core mechanism of modern monetary policy. For the full chain from a central bank decision to your wallet, see how central bank policy reaches the economy.

The framework keeps evolving

In August 2025, the Fed completed its five-year review of its monetary policy framework and quietly retired the “average inflation targeting” experiment it had adopted in 2020. The 2020 version had pledged to let inflation run moderately above 2% after periods below it; after the 2021–2022 surge made deliberate overshoots look beside the point, the Fed returned to straightforward flexible inflation targeting around the 2% PCE goal. The episode is a useful reminder: even the rulebook gets rewritten when reality intervenes.

The number is not the experience

Official inflation is an average, and nobody is average. Housing-heavy households feel shelter costs; commuters feel fuel; the published number reflects neither exactly. Methodology choices — how housing is imputed, how quality improvements are adjusted for — mean the index is the best available estimate with error bars, not a physical constant. Treat it as a compass, not gospel. And when markets convulse over a CPI print, remember: they are not reacting to the price of eggs. They are repricing the future cost of money itself.

Sources: U.S. Bureau of Labor Statistics (CPI methodology, shelter weights, June 2022 inflation report), Federal Reserve (2% PCE target; 2025 framework review via Brookings Institution), Bureau of Economic Analysis (PCE scope), RBC Wealth Management (CPI vs PCE comparison).

This article is educational and is not investment advice.