Recent research shows that hourly payment affects decisions about time use in ways that disfavor uncompensated activities such as volunteering. This paper extends that argument by showing that the activation of money and economics as aspects of a persons self-concept is one mechanism possibly producing these results. Study 1 showed that employed adults explicitly primed to think about their own time in terms of money were less willing to volunteer compared to those primed to think about another persons time in terms of money, illustrating the importance of the self-concept in the economic evaluation of time. Mediation analyses showed that participants view of themselves as economic evaluators fully accounted for both the effect of the manipulation and variation in prior experience with hourly payment on willingness to volunteer. Study 2 showed the undergraduates supraliminally primed with either money or economic concepts were less willing to volunteer their time. The findings suggest that economic evaluation is one causal mechanism affecting attitudes about time use.