Delayed judgment of learning (JOL) is a widely used metacognitive monitoring strategy that can also enhance learning outcomes. However, the potential benefits of delayed JOL on subsequent learning of new material, known as the forward effect of delayed JOL, and its stability and underlying mechanisms have yet to be fully explored. In this study, we investigated the forward effect of delayed JOL using previously unexamined word pair materials and explored the boundary conditions of this effect by manipulating the difficulty of the materials. We also examined this effect within the context of category learning. Our findings demonstrate that delayed JOL significantly enhanced the retention of new information (Experiment 1A), while the forward effect of the delayed JOL occurred only for material with a certain degree of difficulty rather than for easy material (Experiment 1B). These findings were extended and replicated using category learning (Experiment 2). These results suggest that delayed JOL can be used as a preparation strategy for subsequent learning, particularly when faced with challenging materials. Our study provides novel insights into the potential benefits and limitations of delayed JOL and contributes to our understanding of the underlying mechanisms that govern metacognitive monitoring and learning strategies.