That means when this act was passed ie in 2013 the transmission period where alloted to companies ie FY 14 - 15 , 16 - 17 & 17 - 18 . for eg- If term allowed for auditor is for 5 yrs from 2012 & in FY 14 - 15 this act was passed then FY 14 - 15 , 16 - 17 & 17 - 18 will be allowed as transitional period & after FY 17 - 18 ie in 18 - 19 he will be allowed 4 more yrs as he was joined the company in 2012.
FY 14 - 15 , 16 - 17 & 17 - 18 is allowed as transitional period & additional period will be allowed after that for continuation of audit engagement period term allowed.
For private company whose share capital more than 20 crores ( as per recent amendements of mca share capital shall be more than 50cr) total borrowings should execcd 50cr then only the rotation of auditor is applicable to pvt. companies else company can continue with existing auditor