Stellar mass from in situ star formation (blue lines) and ex situ mergers (orange lines) as a function of redshift for central galaxies of four different mass bins at |$z=0$| (⁠|$M_\star \simeq 10^{9.5}, \, 10^{10}, \, 10^{10.5} \, {\rm and} \, 10^{11} \, \mathrm{M}_\odot$|⁠), as labelled. The solid lines and shaded areas show the mean stellar mass growths and standard deviation from the TNG simulation, respectively. The dashed lines show the predictions from decode with the TNG’s SMHM relation as input. The error on the mean, |$\sigma _{\rm std}/\sqrt{N_{\rm gal}}$|⁠, is of the order of 0.01 dex in all the stellar mass bins for both merger and SFHs.