Hard to answer without specific questions. First of all, try to simplify. At the end of the day you are just trying to subtract acquisition price from disposal price for each purchase, to calculate gains. Did you maintain a foreign currency account with deposits/withdrawals independent of the share purchases? If so, you may have to calculate gains on currency separate to shares. If not, then the FX rates are irrelevant. Just use the euro/punt costs of buying shares (assuming you have these to hand) in calculating your gains. Punt to Euro exchange rate is easy -- it's fixed for all time at 1.26974. Tax free allowance is easy -- for shares you are selling this year you have a fixed allowance of €1,270. Indexation (prior to 2003) is a pain, but you just have to look it up from a table. Splits are easy as well: they are covered in Revenue's guides on CGT which you can Google, but basically they change the number but not value of the holding for further calculations. 'Sale and repurchase' I have no clue about.