CG53008 - Substantial shareholdings exemption: interpretation - twelve month period
Paragraph 28 Schedule 7AC TCGA 1992 explains what is meant for the purposes of the substantial shareholdings exemption legislation by a 'twelve month period'. It is a period ending with the day before the first anniversary of the day that started the period. So if a twelve month period started on 18 January 2003 it would end on 17 January 2004.
Parts of days are not taken into account. For instance, if you are testing whether some shares have been held for a twelve month period and the shares were acquired at, say, 15.30 on 18 January 2003 and sold at 09.30 on 17 January 2004 they would still count as having been held for a twelve month period even though they were owned for 6 hours less than a full twelve months.