Why do home value estimates differ so much between websites?
Because each site runs a different model on different data with a different refresh schedule. One leans on county assessments, another on recent nearby sales, another on its own listing history; some update daily, some quarterly. Since your home is off-market while you check, every model is extrapolating — and different extrapolations land tens of thousands of dollars apart. The spread between sites is itself useful information: it approximates the honest uncertainty.
Reviewed · Reviewed by Kristian Peter, CA DRE #01308663
County assessment data — the backbone of most models — varies enormously in quality by county, and in several states assessed value is legally a fraction of market value, which a model must correct for. A model strong in California can be weak in Texas for reasons invisible to the person reading the number.
A practical way to use the disagreement: collect two or three estimates, note the lowest low and the highest high, and treat that as your genuine range going in. Then let pricing sharpen it — agents competing for your listing each stake a projected price with comparables attached, which converts the model spread into defended local judgments.