Dear Pooja,
I agree with Abhishek. It is taken within a block of four years, and you can enjoy two journeys in that block of 4 years. As far as calculation is concerned, one month's basic salary can be considered. Also, 10% of the annual basic can be taken into consideration.
There is no specific rule that is applicable in all companies for LTA. It differs from organization to organization. Since you said you are working, you should definitely have an employee manual or at least rules governing LTA. In our organization, our LTA was for the calendar year. I joined this organization in October of 2008. Since the LTA is for the calendar year, I claimed my LTA for the year 2009 in January itself. In some organizations, it will be clearly written that the employee is eligible for LTA only after completion of one year of service.
Regards,
Vipin:icon1: