How accurate are California price ranges?
Every California figure labelled "Price range" on Groundwork passed a sealed test before it was shown: we priced real sales using only data from before each sale, then compared. Figures labelled "Rough estimate" did not reach that standard; their measured miss is listed too. Where a county's test failed outright, its parcels show no figure.
Tested price ranges
Half within: half of the test sales came within this much of our estimate (the median miss). Inside the range: the share of scored test sales that fell inside the printed range. A range whose final check is not passed by its due date is withdrawn (the parcel then shows facts only).
| County | Priced | Test | Test sales from | Test sales | Half within | Inside the range | Parcels with this range | Final check |
|---|---|---|---|---|---|---|---|---|
| Sonoma County | single-family homes | Sealed home-value test (ca-homevalue-1) | Jul 2025–Mar 2026 | 2,597 | ±9% | 83% | 108,623 | Due Jul 31, 2027 |
| Sonoma County | single-family homes (least expensive tenth) | Sealed home-value test (ca-homevalue-1) | Jul 2025–Mar 2026 | 235 of the 2,597 | ±9% | 80% | 10,229 | Due Jul 31, 2027 |
Rough estimates
Where a county's own sales were too few for a sealed test, or its test missed our standard but stayed usable, the card says "Rough estimate" and gives the miss measured where it was measured: in the county, or across the state's pooled sales. Each label says what it was tested on and how close its estimates came.
| Miss measured | Half within | Covers | Parcels |
|---|---|---|---|
| Riverside County (reassessed values, not sale prices) | ±6% | Land and building | 489,176 |
| Riverside County (reassessed values, not sale prices) | ±12% | Land and building | 50,809 |
| Riverside County (reassessed values, not sale prices) | ±9% | Land and building | 42,292 |
| Riverside County (reassessed values, not sale prices) | ±10% | Land and building | 14,031 |
| Sonoma County | ±19% | Land and building | 11,865 |
| Mariposa County | ±16% | Land and building | 4,633 |
What did not pass
The home-value test (ca-homevalue-1) checked 7 county and home-type groups on 24,116 sealed sales and reassessed values: 1 passed for a price range, 3 passed only as a rough estimate, and 3 passed neither, so they show no tested home value from it.
Land values (ca-value-2): Mariposa County land of 1 to 5 acres, Sonoma County land of 0.25 to 1 acre and Sonoma County land of 1 to 5 acres did not pass on their own test sales (26, 41 and 36 sales), so they are no longer shown as tested ranges. They had shown only because the lot-size classes (0.25 to 1 acre and 1 to 5 acres) passed on the test counties' sales pooled, and Lake County, Mariposa County and Sonoma County each passed with lot sizes pooled. Those parcels now show facts only, with no price range.
A second method, for small residential lots in counties without usable sales, failed its test (its range was too wide), so it shows no figure.
The farmland method was not run, so farmland shows no tested land value.
Sources and dates
Test sales: recorded California sales on file for each county. Test figures: our out-of-time test reports and, where run, sealed final checks (ca-homevalue-1, ca-value-2). Parcel counts: our California map on Oct 24, 2026. Estimates are for your own analysis, not an appraisal or a broker price opinion.