Although monitoring the duration of our actions is essential in many daily activities (driving, playing music, sport etc.), metacognition in the time domain remains poorly investigated. Reaction times constitute a widely used measure of the time taken to decide and initiate an appropriate action. The aim of our study was to examine the contribution of deciding and acting to our ability to subjectively evaluate the duration of our reaction times. In a visual choice reaction time task, participants had to evaluate their reaction time on a visual scale after each response. Electromyography allowed to fractionate reaction times into premotor and motor components. Task difficulty and response force were manipulated to selectively affect these two components. Results suggest that accuracy of metacognition depends on both premotor and motor components variabilities, and that other cues related to experimental factors can be considered to infer reaction times duration.