Article 179
The taxable person shall make the deduction by subtracting from the total amount of VAT due for a given tax period the total amount of VAT in respect of which, during the same period, the right of deduction has arisen and is exercised in accordance with Article 178. However, Member States may require that taxable persons who carry out occasional transactions, as defined in Article 12, exercise their right of deduction only at the time of supply.