Why the Zestimate on Your San Antonio Home Is Usually Wrong — and by How Much

If you are about to list a home in San Antonio and the number you are anchored to came from a Zestimate, a Redfin Estimate, or any other automated valuation model (AVM), assume it is wrong until a broker CMA proves otherwise. In Bexar County the miss is rarely small. On a $350,000 home in a mixed-age neighborhood, a 7–10% error — which is inside the range Zillow itself publishes for off-market homes in many Texas markets — is $25,000 to $35,000. That is the difference between three offers in a weekend and 45 days of price reductions.

This is not an argument that AVMs are useless. It is an argument that they are structurally bad at the specific things that drive price in San Antonio: school-district lines inside the same ZIP, deed restrictions, interior condition, post-sale renovations, and the fact that a meaningful slice of Texas sales data never lands in the public record the way it does in disclosure states.

How the Zestimate is actually built

Zillow's model ingests public tax records (in our case, BCAD data), any MLS feed it has a license to, prior listing history, and user-submitted facts. It then runs a machine-learning model that weights recent nearby sales against your home's reported characteristics. Zillow publishes a median error rate per metro on its "Zestimate accuracy" page, split between on-market and off-market homes. Off-market — which is what you are, until you list — is always worse. Check the current number for the San Antonio metro before you trust any Zestimate; it moves.

The model has three structural problems in Texas:

• Texas is a non-disclosure state. Sale prices are not public record. AVMs get price data from MLS cooperation (SABOR members), not from the county. Any sale that happened off-MLS — FSBO, pocket listing, investor-to-investor, auction, wholesale assignment — is invisible or guessed.
• BCAD's appraised value is not market value. BCAD is constrained by Texas Property Code § 23.23 (the 10% homestead cap) and by mass appraisal methodology. A home with a long-held homestead exemption can be on the tax roll at 60% of what it would sell for. AVMs know this and try to correct, but the correction is a blunt instrument.
• Interior condition is a guess. The model does not know you gutted the kitchen in 2022 or that the foundation has active movement. Photos from a 2017 listing are doing a lot of work it should not be doing.

Where the Zestimate is worst in San Antonio

The error widens anywhere the neighborhood is not uniform. In San Antonio, that is most of it.

78209 — Alamo Heights, Terrell Hills, Olmos Park plus surrounding city blocks

One ZIP, four jurisdictions, three school districts (Alamo Heights ISD, SAISD, and small slivers of NEISD), and lot sizes ranging from 5,000 sq ft bungalows to 1-acre estates. A 1940s 2/1 in Alamo Heights ISD and an identical-on-paper 2/1 six blocks south in SAISD can trade $150,000 apart. The AVM sees "78209, 1,400 sq ft, 2 bed" and averages them. The market does not.

78258 / 78260 — Stone Oak and far north 281

Here the problem is the opposite: tracts look comparable on paper but split between NEISD and Comal ISD, and between city of San Antonio and unincorporated Bexar (different tax rates, different services). Buyers price the district in. The model underweights it.

78204 / 78210 — Southtown, King William, Lavaca, Denver Heights

Historic districts with Office of Historic Preservation review, wild variance in renovation status (a fully restored 1910 Victorian next door to a tear-down), and a lot of off-MLS investor activity. AVMs routinely miss renovated Southtown homes low and tear-downs high.

Anywhere with new construction plus resale mixed

Alamo Ranch (78253), Cibolo, Converse, parts of Schertz. New builds from Lennar, Pulte, and D.R. Horton trade at incentive-adjusted prices that don't reflect true resale value, and those sales drag the AVM on the 8-year-old resale across the street.

Where it is closer — but still not a list price

Uniform master-planned sections inside a single ISD, same builder, same 5–10 year window, same floor plans: the AVM does better. Parts of Redbird Ranch, sections of Bulverde Village, newer Schertz subdivisions zoned entirely to SCUCISD. "Closer" here still means within 3–5%, which on a $400,000 home is $12,000–$20,000. Do not list on that.

What to use instead

A broker CMA built from SABOR MLS

A competent listing agent pulls solds from the last 90–180 days, filters to your subdivision or a defined comp radius, adjusts for square footage, lot, updates, and pool, and hands you a price range with a recommended list. This is the document that should set your number. Ask to see the comps, not just the conclusion.

BCAD's public property search

Free at bcad.org. You cannot see sale prices, but you can see lot size, year built, improvements, and the appraisal district's own value and exemptions. Useful for sanity-checking the characteristics the AVM is using. If BCAD has your home at 1,680 sq ft and Zillow is pricing it as 2,100, that alone explains part of the gap.

A licensed Texas appraiser

Roughly $500–$700 for a residential appraisal in Bexar County as of recent cycles. Worth it when the home is unusual (acreage, custom build, heavy renovation, no clean comps) or when you are in a family dispute, divorce, or estate where a defensible number matters.

What most people get wrong

• Treating the Zestimate range as a confidence interval. It is not a statistical confidence interval. A home shown at "$310K–$395K" is not 95% likely to sell in that band. Ignore the range and look at the published median error for the metro instead.
• Updating the Zestimate with rosy square footage and then believing it. If you tell Zillow your home is 2,400 sq ft when BCAD has it at 2,050, the Zestimate goes up, but a buyer's appraiser will use BCAD and the MLS. You have lied to a model, not to the market.
• Pricing off BCAD appraised value. The tax roll is artificially suppressed by § 23.23 and by the § 11.13 homestead exemption's assessment cap. Market value is almost always higher. Pricing at BCAD leaves money on the table.
• Comparing to active listings instead of solds. Active listings are asking prices. Half of them will be reduced. Only closed sales tell you what a buyer actually paid.
• Ignoring ISD lines inside the same ZIP. A five-minute drive can cross from NEISD to Judson ISD or from NISD to Northside of Medina Valley ISD. Buyers with school-age kids price that at thousands of dollars per point of district rating.
• Assuming the Zestimate went up because your home went up. It may have gone up because three renovated flips closed on your street and the model has no way to know your kitchen is still original.

The practical workflow before you list

1. Pull the current Zestimate and Redfin Estimate. Write them down as data points, not as truth.
2. Pull your BCAD record. Confirm square footage, bed/bath count, and year built are correct.
3. Get a CMA from a SABOR-member agent who works your submarket — not one who works 30 miles away.
4. If the home is unusual, order an appraisal.
5. Set list price based on the CMA, with the AVMs as a sanity check on the low end, not a ceiling.

When you are ready to move, RentInSA can connect you with San Antonio agents who work your specific submarket at /agents, or if you want to sell without a listing commission, you can list your home free at /list-your-home. More pricing and market strategy pieces live at /resources.