Case-Shiller home price index.

In plain English

The Case-Shiller home price index measures home price changes by pairing repeat sales of the same property, so it compares like with like instead of mixing in different houses. S&P Dow Jones Indices publishes a national version plus city composites, each built from public records of homes that have sold at least twice. Because a sale has to close and be recorded before it enters the data, the index arrives on a lag of roughly two months and is reported as a three-month moving average. It measures price change, not price level, so a reading is an index number rather than a dollar amount.

01Why it matters

Home equity is the largest asset most households own, and this index is the cleanest read on whether that equity is growing or shrinking, which shapes decisions about refinancing, selling, and how much a move actually costs.

02The math, step by step

Say a house sells for $300,000, then sells again five years later for $384,000. That pair is an $84,000 gain, or 28 percent over five years, about 5 percent a year. Case-Shiller averages thousands of pairs like that, so one unusual flip does not swing the result.

Illustrative example. The amounts here are hypothetical, chosen to show how the math works, not real quoted rates or figures.

03What this is NOT

04Receipts

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