How Inflation Is Measured
Headlines say inflation was 3.2 percent, but 3.2 percent of what? Here is how the CPI basket works, what core inflation strips out, and why the Fed prefers PCE.
US inflation is measured mainly with the Consumer Price Index, which tracks a fixed basket of household goods and services, and the PCE price index, which the Federal Reserve prefers. Core versions strip out volatile food and energy to reveal the underlying trend. All are reported as year-over-year percent changes.
The CPI basket
The Consumer Price Index tracks about 80,000 prices each month across 200 categories, weighted to match how urban households actually spend. Housing is the biggest slice at roughly a third of the basket, followed by transportation, food, and medical care.
Because it is a fixed basket, the CPI answers a precise question: how much more does the same standard of living cost than a year ago? When the basket that cost $100 last March costs $103.20 this March, reported inflation is 3.2 percent.
What the basket misses
The CPI measures averages, so your personal inflation rate depends on your spending. Renters in hot markets feel housing inflation more than homeowners with fixed mortgages. Households that drive a lot feel gas prices more. The basket is representative, not personal.
It also struggles with quality change. If a laptop costs the same but is twice as fast, statisticians record a price drop, which can feel disconnected from the checkout experience. Substitution is handled too: if beef gets expensive and shoppers buy chicken, the basket gradually reflects the switch.
Core inflation
Headline CPI includes food and energy, which swing wildly with harvests and oil markets. Core CPI strips them out to reveal the underlying trend. A month where gas spikes can push headline inflation up while core stays flat, telling very different stories.
Core is the better guide to where inflation is heading, because food and energy shocks usually fade. But households buy food and energy every week, so headline is the better guide to what life actually costs right now.
Why the Fed watches PCE
The Federal Reserve's 2 percent target refers to the PCE price index, not the CPI. PCE covers a broader basket, including spending by nonprofits and on behalf of households, like employer-paid health insurance, and it handles substitution more gracefully.
PCE inflation usually runs a bit below CPI inflation, roughly 0.3 percentage points lower over long stretches. When you hear the Fed say inflation is near target, check which index they mean before comparing it to the CPI headline.
Reading the monthly report
Each CPI release shows both the year-over-year rate and the month-over-month change. Annualize the monthly number, multiply by 12 roughly, to sense momentum: three straight 0.3 percent months signal inflation running near 3.6 percent annualized, even if the year-over-year figure still looks tame.
Watch shelter, which is the largest component and moves slowly, and services excluding energy, where wage pressure shows up. Goods prices can fall while services keep rising, and that split tells you whether inflation is truly cooling or just hiding.
Skip the arithmetic
Turn an inflation rate into dollars with the free inflation calculator.
Measuring inflation
What is the CPI?
The Consumer Price Index is the Bureau of Labor Statistics' monthly measure of what urban households pay for a fixed basket of goods and services. Its year-over-year percent change is the inflation number most headlines quote.
What is core inflation?
Core inflation is the price index with food and energy removed. Those two categories swing with harvests and oil markets, so removing them reveals whether price pressure is broad and persistent or just a temporary shock.
Why does the Fed prefer PCE over CPI?
The PCE price index covers more spending, including costs paid on households' behalf like employer health insurance, and adjusts for substitution more smoothly. The Federal Reserve defines its 2 percent target in PCE terms, so PCE is the number that drives interest rate decisions.