Expected number of transients similar to AT2017gfo that peak above a given g-, i-, or K-band limiting magnitude. Calculations are based on the black-body model presented in Kasliwal et al. (2017). Solid lines are based on the peak brightness, while dashed and dash-dotted lines are based on the brightness between 4 and 7 days after the merger, respectively. Note that the result for i-band at peak is not shown because it is practically the same as for g-band. The circles and diamonds correspond to the depths of 60- and 180-second exposures, respectively (for LSST in g- and i-band and for VISTA in K-band). The square marker shows the depth of a ZTF 600-second exposure in the g-band. The dashed lines show assumed ranges for GW detections of 75 Mpc for NSNS mergers and 140 Mpc for NS-BH.