Hi Leo,
I just went through the process of calculating this.
Initially I was a bit confused with how to calculate it, but from what I've read you need to treat each investment separately and calculate capital gains on that single buy 8 years later, then add all those capital gains for the year up (using that years exit tax rate), and pay is the subsequent year.
I don't think you can offset exit tax loses (if I'm wrong on this let me know).
I find Excel is the best tool for doing these calculations as you can play around with your own scenarios as needed.
I usually add a few notes to the top for reference as I'm thinking through the scenarios.
I also like to include lots of meta data about the fund so that 8 years down the line I have everything I need.
I'd advise going for an accumulating ETF as if you do a distributing one you'll need to add in the tax on the dividends (dividends from accumulating funds are not taxed in Ireland).
I don't seem to be able to attach any files to this post, otherwise I'd my Excel file with you.
FireDuck