Taxes Consolidation Act, 1997 (Number 39 of 1997)
31 Amount chargeable.
Capital gains tax shall be charged on the total amount of chargeable gains accruing to the person chargeable in the year of assessment, after deducting—
(a) any allowable losses accruing to that person in that year of assessment, and
(b) in so far as they have not been allowed as a deduction from chargeable gains accruing in any previous year of assessment, any allowable losses accruing to that person in any previous year of assessment (not earlier than the year 1974-75).