This is an offering of 2,499,567 shares of our Class A common stock. All of the shares of Class A common stock offered pursuant to this prospectus supplement are to be issued to IBG Holdings LLC in exchange for membership interests in IBG LLC equal in number to such number of shares of Class A common stock issued by us. As a result, we will not receive any cash proceeds from the issuance of such shares of Class A common stock. We do not expect the issuance of Class A common stock to have a material dilutive effect on our stockholders, as discussed below. Our Class A common stock is listed on the Nasdaq Stock Market LLC’s Global Select Market ("Nasdaq") under the symbol "IBKR". On July 29, 2026, the last reported sale price for our common stock was $86.26.