As a self-employed person you need to prepare a set of accounts and therefore need to record all expenses in connection with the work and keep receipts.
All expenses which are wholly and exclusively incurred in the business will be allowable. Any expenses that have some private element (such as motor expenses etc) can be apportioned.
I would reccommend you read the Revenue guide to "starting in Business", and you will also need to consider registering for VAT if your turnover will be over €37,500 in any 12 month period.
You may want to consider getting professional advice, and may also want to consider operating through a Limited Company.
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