Abstract Dominant models of metacognition argue that the quality of sensory information determines perceptual confidence. However, recent accounts suggest that also motor signals contribute to confidence judgments. In line with this assumption, we conducted three pre-registered experiments to investigate the role of the motor preparation of perceptual decisions on confidence. Participants reported the orientation of a Gabor and indicated the level of confidence in their response. A visual cue, displayed before the Gabor, induced the planning of an action that could be congruent/incongruent with the response side and compatible/incompatible with the effector subsequently used to report the Gabor’s orientation. In the three experiments, we observed that confidence consistently increased when participants prepared spatially incongruent actions compared to congruent actions, irrespectively of the effector primed and independently of the correctness of their responses. In the third experiment, electroencephalography recordings (EEG) showed increased P2 amplitude for incongruent compared to congruent actions, suggesting that the planning of incongruent actions led to a larger involvement of early attentional resources required for response inhibition which in turn impacted post-decisional markers of confidence (Error Positivity). Taken together, these findings suggest that motor information might trigger action monitoring mechanisms susceptible to alter confidence in our decisions, implying that motor processes are not only the output, but also an input of the decision process. Significance Statement While virtually every decision we make leads to an action, the role of motor processes in decision making has been largely neglected. Our results show that retrospective confidence in a perceptual discrimination task is boosted when the motor execution is spatially incongruent with motor preparation, independently of the correctness of the response. Electroencephalography recordings indicate that this effect could be explained by a larger involvement of early attentional resources related to action monitoring, which has an impact on confidence computations. Taken together, these results suggest that motor processes might trigger action monitoring mechanisms susceptible to alter retrospective confidence in our decisions, implying that motor processes are not only the output, but also an input of the decision mechanisms.