Prospective memory (PM) refers to the ability to remember to complete a task at the appropriate moment in the future. Past research has found reminders can improve PM performance in both laboratory and naturalistic settings, but few projects have examined the circumstances when and what types of reminders are most beneficial. Three experiments in the present study tested the influence of reminders in an event-based PM task under different cognitive loads. An additional study examined how effective reminders of different types were. In Experiments 1 (specific targets) and 2 (nonspecific targets), load was manipulated by having participants respond to a single (low load) or multiple (high load) targets. In Experiment 3, the association between target-action word pairs was manipulated by presenting strongly associated pairs (low load) or weakly associated pairs (high load). Experiment 4 used target-action word pairs and varied the type of reminder. Participants in the reminder conditions had target (Experiments 1 and 2), target and action (Experiment 3) or target and/or action (Experiment 4) reminders listed at the top of the screen throughout the PM task. Across the first 3 experiments, it was found that the benefit of reminders was greater under high load than low load conditions. Experiment 4 found that target-action reminders improved PM, while target-only or action-only reminders did not. Importantly, the improvements in PM from reminders occurred without cost to ongoing task performance. Together these results suggest that reminders can be beneficial for reducing PM failures, particularly under high load, without the potential downside of increased effort expenditure.