A method by which a first device performs wireless communication is presented. The method can comprise the step of transmitting data through a physical sidelink shared channel (PSSCH) to a second device, receiving, from the second device, hybrid automatic repeat request (HARQ) feedback related to the data through a physical sidelink feedback channel (PSFCH), and acquiring a channel occupancy ratio (CR) for a transmission resource related to the data in a first slot. For example, the transmission resource related to the data remaining after the reception of the HARQ feedback can be released, and the transmission resource related to the data, released after the first slot, cannot be considered with respect to the CR.