Claims are made in tax self-assessments and are checked by the Welsh Revenue Authority (WRA), which has responsibility for ensuring taxpayers pay the correct amount of tax.
Gwneir hawliadau mewn hunanasesiadau treth a chânt eu gwirio gan Awdurdod Cyllid Cymru (ACC), sy'n gyfrifol am sicrhau bod trethdalwyr yn talu'r swm cywir o dreth.