In Ireland, rental income is generally taxable and is normally declared through your annual tax return, even if the property is let for only part of the year. Tax is usually calculated on rental income after eligible expenses, but the rules differ by expense type and some costs may be restricted or disallowed; mortgage interest relief, for example, depends on specific conditions. The resulting income may affect your income tax, USC and PRSI, depending on your circumstances. Keep rent records, invoices and supporting evidence, and check the current guidance on revenue.ie or speak to a tax professional before filing.