What to include in CTC and what not is the prerogative of the HR Function of the company that is decided after discussions and agreement with the management. The key is how you explain the CTC to an employee while hiring. There should be clear communication about this while fixing the salary so as to avoid confusions later.
As a normal term, CTC should include all the monetary benefits given to an employee under various heads, including gratuity. Some companies do not include gratuity part in the CTC, though it is advisable to include. So, components of CTC are decided based on the objectives of the organization as to why they want to project CTC.
Some companies have developed a more expanded form in this respect called "Total Cost To Company (TCTC)" where they capture even the indirect expenses on an employee, viz; pro-rated facility expenses (share of the office premises expenses that are rentals, electricity, other consumables etc.), pro-rated value of work related electronic equipment given to an employee, pro-rated communication expenses, pro-rated expense of employee events / corporate parties, expenses against employee gifts, etc. etc. All these depend on the organizational objective as to what are they going to use this information for.
So, the first step to decide your company's CTC components may be to do a brainstorming with the leadership team and clear the objective as to why you want to introduce this concept.
MK Saseedharan