Total number of black holes per galaxy (N_BH), as a function of stellar mass, for the full population from z = 5 to z = 0. Solid lines show the median in each stellar mass bin, while shaded regions indicate the 5th–95th percentile range. Low-mass galaxies typically host either zero or one BH. The characteristic stellar mass threshold, above which galaxies typically host multiple BHs, shifts to higher masses at later times. This reflects continued stellar mass growth while the formation of new BH seeds declines. In massive systems, N_BH rises steeply with stellar mass due to mergers that build up the BH population.