I am advised by Revenue that the estimated cost of a 1 per cent reduction in Capital Gains Tax (CGT) and Capital Acquisitions Tax (CAT) is as shown in the ready reckoner published at www.revenue.ie/en/corporate/information-about-revenue/statistics/ready-reckoner/index.aspx.
These show a full year cost of €14m for every 1% reduction in CAT and €34m for the same reduction in the CGT. The first year cost is estimated at €12 million for CAT and €31 million for CGT, both assuming the reduced rate is introduced at the start of the tax year. It should be noted that these costs assume no behavioural change.