# What is CPI?

Informational only - not investment advice.

Book: [Reading Financial Data - Step by Step](/guide/)
Chapter: [Economic indicators](/guide/economic-indicators/)
As of: 2026-05-01

CPI is an index that tracks prices for a broad consumer basket.

## Concept

An index is not a dollar amount. CPIAUCSL uses the 1982-1984 average as 100, so the latest number is read against that base. CPI is the level; inflation is the rate of change in that level.

## Worked Example: Read the latest CPI observation

1. Open CPIAUCSL. Its latest observation is 333.979 on 2026-05-01.
2. Because the base period is 100, 333.979 is about 3.34 times the base-period level.
3. A basket of goods that cost $100 in the 1982-1984 base period would cost about $333.98 at this CPI level.
4. A 12-month inflation rate compares the current level with the year-earlier level: 333.979 / 320.62 - 1 = 4.17%.
5. That tells you the index level. It does not by itself say whether any one person's prices changed by that amount.

## See it live

- [CPIAUCSL indicator page](/indicator/CPIAUCSL/)

## Sources

- [CPIAUCSL source](https://fred.stlouisfed.org/series/CPIAUCSL)