Market Quiz: What does CPI actually measure?
Five quick questions on the Consumer Price Index: what it tracks, what 'core' leaves out, and why shelter moves the headline number more than anything else. Answers at the end.
What CPI actually measures
The Consumer Price Index is the most quoted inflation number in the United States, and one of the most misunderstood. The Bureau of Labor Statistics (BLS) defines it as a measure of the average change over time in the prices paid by urban consumers for a market basket of consumer goods and services. The headline version, CPI-U, covers about 93% of the U.S. population. Each month the BLS collects about 80,000 prices from stores, service providers and rental units across 75 urban areas, then sorts them into 8 major groups — from food and housing to medical care and recreation. The result is an index, not a price tag: it shows how the cost of the basket moves, not how much the basket costs. The Federal Reserve's 2% inflation target, for reference, is stated in terms of a different index, the PCE price index from the Bureau of Economic Analysis.
Five questions below test the parts people get wrong most often: what the index counts, what 'core' leaves out, which piece of the basket matters most, who publishes it, and which version decides a retiree's yearly raise. Pick an answer for each, then check yourself at the end.
Question 1 — What does the CPI measure?
Pick the best answer:
A. The average price of everything sold in the United States.
B. The average change over time in the prices paid by urban consumers for a basket of goods and services.
C. The total amount the government spends in a month.
D. The unemployment rate, adjusted for price changes.
Question 2 — What does 'core' CPI leave out?
Pick the best answer:
A. Housing and medical care.
B. Food and energy.
C. Transportation and apparel.
D. Goods — services only.
Question 3 — What is the largest component of the CPI basket?
Pick the best answer:
A. Food and beverages.
B. Transportation.
C. Medical care.
D. Shelter.
- CPI-UCovers about 93% of the U.S. population
- 35.6%Shelter's share of CPI-U (Dec 2025 weights)
- 26.2%Owners' equivalent rent — the biggest single item
- 44.5%Housing's share of the whole basket
- 80,000Prices the BLS collects each month
- 8Major groups in the CPI basket
Question 4 — Who publishes the CPI, and how often?
Pick the best answer:
A. The Federal Reserve, every quarter.
B. The Bureau of Labor Statistics, every month.
C. The Treasury Department, every week.
D. The Bureau of Economic Analysis, every month.
Question 5 — Which index sets Social Security's annual COLA?
Pick the best answer:
A. Headline CPI-U.
B. Core PCE.
C. CPI-W.
D. Chained CPI-U.
Answers — and why
1 — B. The CPI tracks how the cost of a fixed basket moves over time. It is an index of change, not a price level.
2 — B. Core CPI strips out food and energy, whose prices swing the most, to show the underlying trend. Headline CPI still includes them.
3 — D. Shelter is 35.6% of CPI-U by the BLS December 2025 weights, and owners' equivalent rent alone is 26.2%. Housing as a whole is 44.5%.
4 — B. The BLS publishes the CPI every month, collecting about 80,000 prices. The BEA publishes the PCE index, the measure behind the Fed's 2% target.
5 — C. By law, the Social Security cost-of-living adjustment uses CPI-W, which covers urban wage earners and clerical workers — roughly 30% of the population.
How did you do? Five out of five means you read inflation headlines like a pro; three or fewer means the next CPI release is worth reading twice. Educational content, not investment advice.
