In your case rough calc ( since asset bought post 2003 ) would be :-
Selling price minus costs associated with sale (legal/auctioneer etc)
= net sale proceeds
Purchase price + costs associated with purchase (s/duty/legal etc) + any enhancement expenditure (not already claimed against income tax)
= total cost
Net sale proceeds minus total cost = chargeable gain
chargeable gain minus personal exemption (€1,270 or €2,540 if joint owned) = taxable gain
taxable gain x 20% = cgt due