The calculation of the number of years since the creation of the Universe as well as the number of years till the dissolution of the Universe has been done by the Sages in India. Sage Vasishtha has mentioned that the creation of the Universe happened 34.5 billion years ago.
The creation of the Universe happened on the hindu Calendar Date (tithi) of Chaitra Shukla Pratipada. Thus, the hindu calendar begins on the sunrise of this tithi. This date usually falls on any day from late march to mid-April on the Gregorian calendar. india is the spiritual guide of the world; hence the Sages have the Divine capability to calculate the time span since the beginning of the Universe. Just as one year is divided into 12 months, each month is divided into 30 or 31 days, each day is divided into 24 hours and so on