appears to have solidified its place as the No. 2 portal in the U.S. market, without a corresponding decline in traffic at any other portal.

Why it matters: Portal traffic appears to be a non-zero-sum game — traffic gained by one portal is additive and not coming at the expense of other portals.

Dig deeper: In the first quarter of 2023, the big three real estate portals — Zillow,, and Redfin — had a combined 334 million average monthly unique visitors.

  • Fast forward to the first quarter of 2024 and those same portals have a combined 338 million average monthly uniques — no change — with growing to an additional 94 million average monthly uniques.

And that’s just for — if you include CoStar’s entire residential network, which includes, the scale is even greater.

  • It’s a valid comparison; the other portals also include traffic from a larger network of sites, including rentals.
  • The result is that CoStar’s resi network has nearly double the traffic of

CoStar’s traffic reporting hasn’t been consistent — it has fluctuated between and the entire residential network, and sometimes includes quarterly averages and other times specific months.

  • CoStar’s inconsistent reporting runs the risk of reducing trust in its traffic numbers, even when the underlying results are impressively real.
  • But traffic has unequivocally increased over the past year, punctuated by two periods of heavy advertising.

CoStar’s advertising spend reached an all-time high in Q1 2024 — which directly corresponds to the recent traffic surge in February and March.

The bottom line: While’s traffic increase is additive to the market and not affecting other portals’ traffic, that’s not to say it won’t affect their businesses.

  • Unlike website visits, there is a finite amount of transactions, commission dollars, and agents willing to spend money online; that’s a zero-sum game.

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