Systems, apparatus, methods, and computer-readable media that enable and support backward cancellation indication for sidelink transmissions are described. In a situation where a sidelink data transmission with respect to one or more resources previously reserved for sidelink communication is ineffectual, a sidelink transmission user equipment (UE) may indicate the ineffectual data transmission in a transmission opportunity subsequent to the transmission having an ineffectual data transmission, such as by transmitting a backward cancellation indication (BCI). The BCI may provide information to a corresponding sidelink receiver UE regarding the resource with respect to the ineffectual data transmission. The sidelink receiver UE may use information provided by the BCI in determining whether to alter utilization of signals received on resources of the ineffectual data transmission. Other aspects and features are also claimed and described.