X0306 4 2018-08-14 0001278021 MARKETAXESS HOLDINGS INC MKTX 0001296468 Themelis Nicholas C/O MARKETAXESS HOLDINGS INC. 299 PARK AVENUE NEW YORK NY 10171 0 1 0 0 Chief Information Officer Common Stock, par value $0.003 per share 2018-08-14 4 S 0 11394 186.4459 D 43333 D Common Stock, par value $0.003 per share 2018-08-14 4 S 0 1437 187.0071 D 41896 D The transactions were executed in multiple trades at prices ranging from $185.88 to $186.83. The price above reflects the weighted average sales price. Detailed information regarding the number of shares sold at each separate price will be provided upon request by the Commission staff, the Issuer or a security holder of the Issuer. The transactions were executed in multiple trades at prices ranging from $186.94 to $187.07. The price above reflects the weighted average sales price. Detailed information regarding the number of shares sold at each separate price will be provided upon request by the Commission staff, the Issuer or a security holder of the Issuer. /s/ Ori Solomon, as Attorney-in-Fact for Nicholas Themelis 2018-08-16