As the devolved taxes operate on a basis of self-assessment, taxpayers are required to take the provisions of the GAAR into account when completing their tax returns.
Gan fod y trethi datganoledig yn gweithredu ar sail hunanasesu, mae'n ofynnol i drethdalwyr ystyried darpariaethau'r GAAR wrth lenwi eu ffurflenni treth.