Why Your Appraisal Value Might Differ From Zillow (And Why That's OK)
I get this question at least once a week: "Zillow says my house is worth $X, so why did the appraisal come in different?" It is a fair question, and the answer comes down to how automated valuation models work versus how a trained appraiser determines value.
How Zillow's Zestimate Works
Zillow uses an automated valuation model (AVM) that pulls from public records, tax assessments, and recent sales data. It runs those numbers through an algorithm and spits out an estimate. The Zestimate updates regularly and covers virtually every residential property in the country.
The problem is what the algorithm cannot see. It does not know that you renovated your kitchen last year. It does not know that the comparable sale down the street sold low because it was a divorce situation. It does not know that your neighbor's pool is twice the size of yours, or that the home across the street has a foundation issue. All of those things affect value, and none of them show up in public records.
What an Appraiser Does Differently
When I appraise a home, I physically inspect it. I see the updated bathrooms, the new roof, the cracked driveway, the view from the back porch. I drive the neighborhood and note what is selling, what is sitting, and what is under construction. Then I select comparable sales — not based on an algorithm, but based on my knowledge of which homes are truly similar to the subject.
I also make specific adjustments. If a comparable sale has a pool and the subject does not, I adjust for that. If one comp is on a busy road and the subject is on a cul-de-sac, I adjust for that too. An AVM cannot make those judgment calls because it does not have eyes on the property.
When the Numbers Disagree
Zillow's own data shows that the Zestimate has a median error rate of around 2-3% for on-market homes and 6-7% for off-market homes. On a $350,000 house, that is a potential swing of $21,000 to $24,500. That is a big number when you are trying to price a home for sale or determine if you have enough equity to refinance.
In my experience, the Zestimate tends to lag in rapidly changing markets. When prices are rising quickly, it underestimates. When the market cools, it overestimates. It also struggles with unique properties, waterfront homes, and rural areas where there are fewer data points to work with.
So Which One Is Right?
Neither is perfect, but an appraisal is the only one that a lender, court, or government agency will accept as an official opinion of value. The Zestimate is a useful starting point for a general sense of where values are, but it was never designed to replace a professional appraisal.
If your appraisal came in lower than Zillow, it does not necessarily mean something is wrong. It might mean the Zestimate was including data from a neighborhood with different characteristics, or it had not yet factored in a market slowdown. If your appraisal came in higher, same thing — the algorithm may not be capturing improvements or location advantages that a human appraiser can see.
The Bottom Line
Use Zillow for ballpark estimates. Use an appraisal when the number actually matters — when money is on the line, when you are making a financial decision, or when someone needs an independent, defensible opinion of value.
Questions about your property's value? Contact us or call 904-510-3398.