X0306 4 2019-04-26 0 0001278021 MARKETAXESS HOLDINGS INC MKTX 0001296468 Themelis Nicholas C/O MARKETAXESS HOLDINGS INC. 55 HUDSON YARDS, 15TH FLOOR NEW YORK NY 10001 0 1 0 0 Chief Information Officer Common Stock, par value $0.003 per share 2019-04-26 4 S 0 1489 265.611 D 53564 D The transactions were executed in multiple trades at prices ranging from $265.32 to $266.22. 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/ Jason Edelstein, as Attorney-in-Fact for Nicholas Themelis 2019-04-29