Mutual mate choice is prevalent in humans, where both males and females have a say in their choice of partner. How the choices made by one sex constrain the choice of the other remains poorly understood, however, because human studies have mostly limited themselves to measuring preferences. We used a sample of 5782 speed-daters making 128 104 choices to link preferences for partner height to actual choice and the formation of a match (the mutual expression of interest to meet again). We show that sexual conflict at the level of preferences is translated into choice: women were most likely to choose a speed-dater 25 cm taller than themselves, whereas men were most likely to choose women only 7 cm shorter than themselves. As a consequence, matches were most likely at an intermediate height difference (19 cm) that differed significantly from the preferred height difference of both sexes. Thus, our study reveals how mutual mate choice can result in suboptimal pair formation for both sexes, highlighting the importance of assessing the mate choice process in its entirety.