The claim must be made by the later of 1 May 2029 (4 years from the filing date for the return to which the claim relates) or 31 March 2030 (12 months after the reconsideration date).
Rhaid hawlio erbyn 1 Mai 2029 fan bellaf (4 blynedd o ddyddiad ffeilio’r ffurflen dreth sy’n berthnasol i'r hawliad) neu 31 Mawrth 2030 (12 mis ar ôl y dyddiad ailystyried).