Applicability of Income Tax audit - sec 44 AB
Income tax audit is applicable in case the gross turnover or gross receipts from a business exceeds Rs.1 crore, gross receipts from profession exceeds Rs.25 lakhs in a year.
The Gross turnover or receipts should be calculated on a inclusive basis ie., the vat or service tax or excise duty should also be included while taking into consideration the turnover amount.
Further the audit is also applicable if the assessee shows net profit less than 8% of turnover though he is covered u/s 44AD
Tax audit is applicable if assessee have 4 different type of business and turnover does not cross 1 crore in each business but on consolidation the turnover exceeds 1 crore?
In your case tax audit is applicable since to calculate turnover, turnover from all the business should be combined. Hence if turnover exceeds 1 crore from 4 businesses then tax audit is applicable.
Further to add on trade discount, sales returns can be excluded to arrive at gross turnover.