In very simple terms, based on the brief information that you've posted, you should be entitled to CGT relief in relation to the 7 years that it was your PPR and also the final year of ownership - i.e 8 years in total. So it's likely that (21 - 8) / 21 = 62% of the total gain is actually liable for CGT. As mentioned above certain expenses may be allowable when calculating the gain. And since the property was acquired in 2003 the original base cost may be indexable for inflation. The Revenue summary information linked above and the further information guides give more information. But, if in doubt, get independent professional advice.