Author summary Sensing the passage of time is a common experience of our everyday life activity. Even without a watch, we can, for example, tell whether the bus we are waiting for is late. The neuronal mechanism that enables us to sense the passage of time is largely unknown. Here, we asked healthy human volunteers to discriminate between visual events of varying durations while we measured brain activity via functional magnetic resonance imaging (fMRI). The results show that distinct portions of the supplementary motor area (SMA)—a region of the cerebral cortex important for both motor preparation and time perception—respond preferentially to different durations. The portions of the SMA responding to similar durations are in close spatial proximity on the cortex, and their response is greater for preferred and neighboring durations and suppressed for distant ones. The spatial arrangement of duration-selective portions of the SMA could be the mechanism that enables us to efficiently sense that a certain duration has elapsed.