With regard to shares bought and sold within a 4 week period any loss cannot be offset against other CGT gains (apart from the same shares reacquired in the same 4 week period)
This page is an explanation of the special rules that apply to CGT on shares
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Does this rule only apply to shares or does it also apply to options which by their nature are for shorter duration? for instance if an option contract expires within 3 weeks, can any loss be offset against other CGT gains?