A method for a first device to perform wireless communication based on partial sensing and an apparatus supporting the same are provided. The method may comprise: triggering a resource selection procedure; determining a selection window within a packet delay budget (PDB) based on the triggering of the resource selection procedure; selecting Y candidate slots in the selection window; performing sensing within a contiguous partial sensing (CPS) window related to the Y candidate slots; and selecting a sidelink (SL) resource based on random selection within the selection window, based on the number of slots included in the CPS window which is less than a minimum number of slots, wherein Y is a positive integer.