Preparing for the future during ongoing activities is an essential skill. Yet it is currently unclear to what extent we can prepare for the future in parallel with another task. In two experiments, we investigated how characteristics of a present task influenced whether and when participants prepared for the future, as well as its usefulness. We focused on the influence of concurrent working memory load, assuming that working memory would interfere most strongly with preparation. In both experiments, participants performed a novel sequential dual-task paradigm, in which they could voluntarily prepare for a second task while performing a first task. We identified task preparation by means of eye tracking, by detecting when participants switched their gaze to information about the second task while performing the first task. The results showed that participants prepared, but also that there were large individual differences in how often they did so. When participants prepared, it was productive, as evidenced by faster RTs on the second task and only a small cost to the present task. The probability of preparation and its productiveness decreased with increases in the difficulty of the first task. In particular, we found that working memory load from the first task interfered with preparation. We conclude from our study that people can productively prepare for the future while performing an ongoing task, and that it is possible to track this preparation process empirically. In addition, we conclude that working memory resources play an important role in task preparation.