Unless it is a Revenue approved scheme that allows for some tax deferrals (your employer should be able to tell you) then you are liable for income tax at your marginal rate (20% or 41%) on the nominal gain attributable to the discounted price (i.e. the difference between the market value at the time of exercising the options and the discounted price). This is payable within 30 days via an [broken link removed]. After than if you hold onto them and sell for a gain with respect to the market value at the time of acquisition then CGT at 20% applies on the gain less any allowable expenses and exemptions.