Generally for the Govt. Jobs applicants are being asked to calculate age as on cut off date.
For Example you are going to apply for SSC Exam and requirement is that you should be between
18-28 years (in case of General Category) as on 1 January 2014 assuming that your Birth falls on
15 August 1986. So in This case
“First Date” or “Your Date of Birth” : 15 August 1986
“Second Date” or “As on Date” : 1 Jan 2014
So your actual age is 27 Years 4 Months 15 days. So you are eligible to apply.