Your Receipt and the CPI Are Both Right — The Gap Is the Story

You stand at the checkout watching the total climb, and the receipt says thirty-eight dollars for what cost twenty-five two years ago. The news says inflation is three percent. Both are true. They are measuring two different things.

How the official number is built

The CPI starts with a basket — about 400 items, surveyed across 80 urban areas, thousands of price checks a month. Bread, rent, gasoline, haircuts, prescription drugs. Field agents record the price of the same white bread in Cleveland, the same unleaded in Phoenix, month after month.

But not every item counts equally.

The substitution assumption

Here is the first catch. CPI assumes you will substitute. When steak spikes, the formula expects you to switch to chicken. Name-brand cereal too expensive? You buy generic. That assumption is reasonable on average — and it quietly lowers the measured rate.