How home value estimates work
An estimated present value, computed only from public records, shown as a range. Currently covers 11,257 Zionsville-area homes, refreshed Aug 1, 2026. It is a starting point, not an appraisal.
The method
Every number comes from two public sources: the county assessor's valuations and recorded sale prices (Indiana is a disclosure state, so real sale prices are public). Two independent reads are blended:
- Assessment, corrected by the market. The assessor values every home on one date, which makes assessments good at ranking homes and imperfect on level. We measure that gap directly: the ratio between recent recorded sale prices and those homes' assessments, in the same neighborhood where sales allow (widening to school zone or town when they don't, and separately for condos). The home's assessment times that observed ratio is the first read.
- The home's own last sale, brought forward. A monthly Zionsville price index, built from all recorded sales, moves the home's most recent sale price to today. The more recent the sale, the more weight this read carries.
When the two reads disagree severely, or a home's records can't support either one, no estimate is shown at all.
What the likely range means
The headline is the single most-likely figure. The likely range under it is the middle-half band: in backtesting, half of actual sale prices fell inside it and a quarter landed on either side. It is tighter (about ±8%) where the home's own neighborhood has enough recent sales, wider (about ±11%) where the comparison pool is broader. Three quarters of sales fell within a wider ±16% of the estimate. Records can't see renovations, condition, or a buyer's circumstances, so single homes can and do land outside any band.
Measured accuracy
Before showing a single estimate, the model was backtested against 692 recorded sales from January 2025 through mid-2026, each predicted using only information available the day before it sold:
| Median error | 8.9% |
| Sales predicted within 10% | 56% |
| Sales predicted within 20% | 84% |
| Sales inside the likely range (the middle-half band) | half, by design |
Assessments update once a year, so accuracy is best right after a new assessment file and drifts as it ages: on 2026 sales alone, predicted with a year-old file, the median error was 10.3% and 70% fell inside the range. The backtest is re-run after each annual assessment load.
Homes with no estimate
About a quarter of homes show none, on purpose: new construction the assessor hasn't valued yet, parcels whose assessment is mostly land value, and homes whose latest recorded transfer was unusual (multiple parcels, non-market terms) in a way that would contradict the estimate. Showing nothing beats guessing.