The main rate of Corporation Tax for 2015 is 20% (With the exception of oil and gas companies with ring fence profits) from 1 April 2015. The Corporation Tax will be charged at a single rate known as the main rate. The small profits rate was abolished with effect from 1 April 2015 when it was unified with the main rate. The rates for ring fence profits are unchanged. A new version of the CT600 (version 3) and guide will be published in April 2015. The CT600 Version 3 return must be used for periods that start on or after 1 April 2015 and HMRC systems will be able to accept returns for this period from 6 April 2015.