When given a choice, people will avoid cognitively effortful courses of action because the experience of effort is evaluated as aversive and costly. At the same time, a body of work spanning psychology, economics, and neuroscience suggests that goods, actions, and experiences are often evaluated in the context in which they are encountered, rather in absolute terms. To probe the extent to which the evaluation of cognitive effort is also context-dependent, we had participants learn associations between unique stimuli and subjective demand levels across low-demand and high-demand contexts. We probed demand preferences and subjective evaluation using a forced-choice paradigm as well by examining effort ratings, taken both on-line (during learning) and off-line (after choice). When choosing between two stimuli objectively identical in terms of demand, participants showed a clear preference for the stimulus learned in the low- versus high-demand context and rated this stimulus as more subjectively effortful than the low-demand context in on-line but not off-line ratings, suggesting an assimilation effect. Finally, we observed that the extent to which individual participants who exhibited stronger assimilation effects in off-line demand ratings were more likely to manifest an assimilation effect in demand preferences. Broadly, our findings suggest that effort evaluations occur in a context-dependent manner and are specifically assimilated to the broader context in which they occur.