Homes that appeared on Zillow sold for 1.3% less, on average, than comparable listings that did not show up on the portal, according to new internal research from Compass International Holdings.
The analysis, led by Compass chief economist Mike Simonsen and chief data officer Dave Crosby, examined 296,966 Compass listings posted between January 2025 and May 2026. Of those, 806 listings were “banned” from appearing on Zillow. The median sale-to-list price ratio for banned listings was 100%, compared with 98.7% for non-banned listings, Compass said.
On a $1 million home, a 1.3% gap equates to roughly $13,000 in seller proceeds. Compass refers to this difference as the “Zillow Tax.” The firm argues that, while Zillow has long promoted rapid online exposure as critical to a sale, the net effect of appearing on the site is a lower achieved price for sellers.
This study from Compass comes as the two firms are engaged in an on going legal battle. After Zillow’s Listing Access Standards policy went into effect last June, Compass filed an antitrust lawsuit against the listing portal giant claiming that it was using its monopoly power to harm Compass and industry competition.
Compass voluntarily dismissed the lawsuit in March, just to have Zillow file its own antitrust in May, in which Zillow claims the brokerage firm and Midwest Real Estate Data (MRED) conspired to cut off the Chicagoland MLS’s data feed to Zillow.
A House Judiciary subcommittee is also now pressing MRED and Compass to explain their nationwide private listing network partnership. Additionally, earlier this month Compass filed Code of Ethics complaints, which allege that Zillow has made false advertising claims, in 26 states, 55 MLSs and 30 Realtor associations.
How Compass measured the ‘Zillow tax’
Using quantile regression, Compass economists found the 1.3 percentage point difference in sale-to-list ratio between Zillow-banned and non-banned listings to be statistically significant, with a margin of error of plus or minus 0.8 percentage points.
The company also reported that 50.5% of banned listings sold at or above list price, versus 44.6% of non-banned listings. That 5.9 percentage point spread (± 5.6 percentage points) was also deemed statistically significant. Compass said these trends held after controlling for market, price point, agent and pre-marketing strategy.
At the same time, the research found no meaningful difference in the likelihood or speed of a home going under contract based on whether it appeared on Zillow. For listings banned by Zillow, 34% went under contract within 30 days, compared with 36% of non-banned listings. The raw difference of -2.1 percentage points fell within a margin of error of ± 3.3 percentage points and was statistically insignificant, according to the report.
When Compass controlled for market, price and agent, the difference shifted to 2.5 percentage points (± 3.2 percentage points), which also remained statistically insignificant, the firm said in its report. The company said it measured pending rates across multiple time horizons and did not find a significant performance gap between Zillow-banned and non-banned homes.
Why Compass says Zillow can pressure prices
In its report, Compass characterizes Zillow primarily as a lead-generation platform that advantages buyers at the expense of sellers, rather than a tool designed to protect home values. The company points to several consumer-facing features that it says can weigh on offers including days on market, price cut history, climate risk data and Zillow’s Zestimate.
Compass argues that sellers can mitigate the so-called Zillow tax by adopting a phased marketing strategy — like its three-phased marketing strategy — building interest, collecting feedback and creating urgency before exposing the property to broad portal audiences and public days-on-market counters.
Zillow did not immediately respond to HousingWire’s request for comment.
Zillow’s data
In recent court filings in its antitrust lawsuit against Compass and MRED, economist Lawrence Wu, an expert witness Zillow brought in for the hearing on its preliminary injunction motion earlier this month, wrote that his analysis found that sales made via Compass’s private listing network were associated with 4% lower price in Chicagoland and 4.8% lower price nationally compared to listings that were not sold on Compass’s private listing network
Wu’s analysis was based on Zillow’s transaction data from January 2022 through December 2025. The firm said it identified what it believed to be Compass private listing network sales from properties that entered the MLS as sold or were recorded as sold within one day, with Compass agents on both sides of the transaction.
This article was written by Brooklee Han and generated with the assistance of HousingWire Automation, then reviewed by a HousingWire editor before publication.
