Several hands grab for a second-place medal.
Illustration by Lanette Behiry/Real Estate News; Shutterstock says it's second to Zillow, but does the math add up? 

A exec told Real Estate News that its “playbook for growth is working,” but some competitors and outside observers see the data differently.

Updated October 5, 2023
5 minutes

Key points:

  • CoStar says exceeded 100 million unique visitors in September.
  • Spokespeople from Zillow and said’s claims rely on data comparisons that are difficult to independently verify.
  • Some data from web analytics firm Similarweb supports’s claim.
  • “We are very clearly going for number one,” said President Dave Mele.

This week, CoStar announced that had more than 100 million unique visitors in September, declaring itself the second-most visited residential real estate portal after Zillow and ahead of and Redfin. 

And now it has set its sights on the No. 1 spot.

This represents a massive jump in traffic just in the past couple of months, which to CoStar, signals that its investment in is paying off. 

But Zillow and take issue with CoStar's math. And some third-party data showed trailing behind its main rivals. 

Celebrating silver, going for gold

CoStar has been clear about its intention to take to the top spot. In May, CEO Andy Florance told Real Estate News that could become the second-most visited portal within 12 months. But now, the real estate giant says that they have achieved that goal much sooner. 

"I think what it means is that the playbook for growth is working," Dave Mele, president of, told Real Estate News. That playbook includes a big advertising push, hiring a team solely focused on creating original content for the site, and an effort to differentiate itself from the competition by positioning as being friendlier to both agents and consumers

Mele told Real Estate News that traffic more than doubled between August and September, going from 39.2 million unique visitors in July to 46.3 million uniques in August, and then just topping 100 million in September. Mele said that these figures came directly from Google Analytics.

But CoStar isn't content with second place, Mele said, vowing to keep pushing until bumps Zillow out from the top spot. 

"Historically, there have been players who may have been satisfied with being number two or number three. We aren't," Mele said. "We are very clearly going for number one. It's our goal to be number one." 

Competitors question data comparisons

There is no easy way to independently verify CoStar's numbers. According to data shared with Real Estate News by Similarweb, a web analytics firm, logged 39.8 million unique visitors in September, ahead of Redfin, which had 32.9 million. came in second with 45.5 million unique visitors and Zillow had 90.41 million.

Media analytics company Comscore also shared its latest numbers with Real Estate News, showing that in August, Zillow received 109.5 million unique visitors, had 56.5 million, Redfin had 37 million, and tallied 33.3 million. A Comscore spokesperson said that September traffic estimates won't be available until mid-October.

But there's no doubt that has been gaining ground, however. When looking at year-over-year growth, Similarweb's data shows led the pack by a longshot, seeing its visits increase by 639% since September 2022, versus 7.2% for Redfin, 7.3 % for Zillow, and -3.3% for

And when the Similarweb data is sliced by de-duplicated users — the number of users driving traffic to a website across multiple devices, but counted only once — moves into the second place spot ahead of Redfin and By this measure, which is still in beta, Raymond "RJ" Jones, VP of investor relations at Similarweb, told Real Estate News that is "getting new unique users to the site and taking share from pretty much everyone."

CoStar staked its claim on No. 2 by comparing numbers to publicly reported three-month aggregate traffic numbers from competitors' quarterly earnings. But a spokesperson for Zillow told Real Estate News that it's not apples to apples. This makes it difficult to construe what an individual month's traffic actually was, they said. also took issue with the comparison. "It's difficult to understand the consistency of their calculations," a spokesperson said to Real Estate News. "What we do know is that has held audience share based on independent ComScore data across the last four months, and our audience has the highest intent to either buy or sell a property." vows to 'compete very hard' for consumer attention

When asked about third-party web traffic data, Mele said those sites don't always tell the full story and can misrepresent the actual traffic websites are getting. 

"What we know about third-party sources is that they tend to lag and underrepresent growing sites," he said. "They try to smooth the growth, they try to manage traffic spikes and increases."

However, Mele does acknowledge that the contest among top portals is for a "finite number of actual home buyers and sellers," adding that the battle for attention from users and agents is at some point "going to be a zero sum game."

It's a theme that even former Zillow CEO Spencer Rascoff has acknowledged, particularly as the class action lawsuits against NAR and top brokerages loom over an industry that is bracing for what could be a "seismic shift" in cooperative compensation, impacting everyone from individual agents, to brokerages, to home search sites.

"You do have to compete to win," Mele said to Real Estate News. "And so yeah, you do have some giants who are competing and we're gonna compete very hard. And the good news is we have the commitment and the resources to do that."

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