Keep purchase and sale contracts, solicitor and estate-agent statements, stamp duty and Local Property Tax records, mortgage statements, rent received, expense records, and invoices for repairs or improvements. Also note important dates, ownership shares and correspondence with Revenue, keeping electronic copies where appropriate. These records may be needed to support a tax return or calculate a gain, but not every property cost is treated the same way for tax. Retention requirements can vary, so check the latest guidance on revenue.ie or speak to a qualified tax professional.