CoStar Group (CSGP): the founder-CEO bought three times as the stock fell 62%

CoStar Group, the commercial real estate data and marketplace company, closed at $79.00 on October 8, 2025 — its highest close of the following twelve months. On October 8, 2026 it closed at $29.81, down 62.3%. The low came on September 29, 2026, at $26.95. During that fall, its founder and chief executive bought shares on the open market three times, each time at a lower price.

Three rounds, each cheaper

Andrew C. Florance is described as “Founder and Chief Executive Officer” in CoStar’s January 7, 2026 filing, and the company’s proxy statement says he founded it in 1987; it went public in July 1998. His three purchases, all reported on Form 4 with transaction code P (an open-market purchase) and held in his direct account:

This was not buying at the bottom. After each round the stock kept falling, and after the August purchase it dropped another 9.8%, to the September 29 low. At the October 8 close, the shares he bought were worth $6.27 million — 16.2% less than he paid.

The timing follows the earnings calendar. Each purchase came a few trading days after a quarterly results release: the third trading day after the February 24 report, the third after April 28, and the fifth after July 28. The stock fell on the first trading day after each of the four results releases in the period — 9.9% in October 2025, 8.9% in February, 5.1% in April and 1.6% in July. The filings do not say why Florance bought, and they do not explain why the stock fell, so neither does this article.

Others who bought, and who sold

Three other insiders bought in early March 2026: Frederick Saint, president of marketplaces, bought 20,000 shares at $45.33 ($906,600), and directors Rachel Glaser and Louise Sams bought 1,000 shares each. In total, four insiders made seven open-market purchases worth $8.48 million.

Insider selling was small: four sales by director John Hill and chief accounting officer Cynthia Cann, $534,000 in total, two in November 2025 and two in August 2026. Florance sold no shares on the open market in the twelve months.

Not every Form 4 line is a purchase. A March 10, 2026 entry of 124,162 shares for Florance (code A) came from the company’s Management Stock Purchase Plan, which converts part of an executive’s cash bonus into deferred stock units and adds restricted units — compensation, not a market purchase. Code F lines are shares withheld by the company to pay taxes, and a February code D line is performance shares forfeited when the payout was certified. None of these are sales either.

The company was buying too

CoStar repurchased $500 million of its own stock in 2025 and $587 million in the first half of 2026, under a $1.5 billion program announced on January 7, 2026 — a day on which the stock fell 8.2%. Shares outstanding went from 423,822,791 in October 2025 to 405,197,588 in July 2026, a 4.4% reduction.

In the same period CoStar was a buyer of another company, not a target: it agreed on May 28, 2026 to buy Zonda for $800 million and completed the deal on August 21.

How much he owns

After the August purchase, Florance’s direct account held 1,806,165 shares, worth $53.8 million at $29.81 and equal to 0.45% of the company. The proxy statement, as of April 1, 2026, lists 3,044,568 shares of beneficial ownership — less than 1% — including 1,393,133 exercisable options and 627,814 restricted shares. The same proxy notes that the CEO’s minimum stock-ownership requirement was raised from six to ten times base salary; no filing connects that rule to his purchases.

A purchase shows what an insider did with their own money; it is not a forecast. The CoStar page shows the price history and fundamentals, and the insiders page lists open-market trades across the market as they are filed. Not investment advice.