All murder convictions must result in a life sentence and the court determines the appropriate minimum term to be served in custody in each case before the offender can be considered for release on life licence by the Parole Board. The average time spent in custody before release by offenders serving mandatory life sentences for murder has increased from 13 years in 2004 to 17 years in 2014.
The average time served in custody by people convicted of murder in each of the last five years is not known. Information is available in relation to offenders serving mandatory life sentences for murder who have been released in the last five years. This is included in the Offender Management Statistics Quarterly, Prison Releases Annual Tables, Table A3.3 “Number of first indeterminate releases and average time served”: https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/424903/prison-releases-annual-2014.xlsx .