How do students decide what major to study and what explains the low enrolment of women in science and economics? Using data on the subjective expectations of undergraduate students who are in the process of selecting a major, we model major choice as a function of major-specific and job-specific attributes. We identify significant gender differences in the preferences for different attributes as well as in the expectations of future outcomes, especially of grades. Women are willing to pay twice as much as men for course enjoyment and higher grades, even as they expect lower grades in science and economics. This suggests that in addition to gender differences in preferences being shaped by pervasive norms about which subjects are considered more suitable for women, women also suffer from a relative confidence gap in their major-specific abilities.