Where a taxpayer has made a return and there is an amount of tax payable, that amount of tax must be paid by the taxpayer, no later than the filing date for the return.
Os bydd trethdalwr wedi cyflwyno ffurflen dreth a bod swm o dreth yn daladwy, rhaid i'r trethdalwr dalu'r swm hwnnw o dreth, erbyn dyddiad ffeilio'r ffurflen dreth fan hwyraf.