The question you need to answer is whether or not you are a "chargeable person". If you are a chargeable person then you must file a Form 11 tax return (i.e. self-assessment), if you aren't a chargeable person then you can file a Form 12 / use PAYE anytime...
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Non-PAYE income less than €50,000 gross
An individual who is in receipt of income chargeable to tax under the PAYE system but who is also in receipt of income from other non-PAYE sources will not be regarded as a "chargeable person" if the total gross income from all non-PAYE sources is less than €50,000 and the net assessable income is less than €3,174 and the income is coded against PAYE tax credits.
There is no change to the current practice in relation to individuals who fall within this category, provided they have assessable non-PAYE income of less than €3,174. These individuals can continue to have the liability on such income effectively assessed within PAYE by means of coding in the income against their tax credits.
Assessable non-PAYE income of €3,174 or more
An individual with assessable non-PAYE income of €3,174 or more for any year is regarded as a "chargeable person" for Self-Assessment and must file a Form 11 for that year.