Why do we count the age of Islam from the beginning of the Hijrah and not from the beginning of the revelation and the call?

Title: Why do we count the age of Islam from the beginning of the Hijrah and not from the beginning of the revelation and the call?

Language: English

Short Discription: This is a questioned answered by the Permanent Committee regarding, I hope insha allah this question reaches u in good health. My question is I have noticed when a non muslim asks about the age Islam after prophet hood we as Muslims answer only with the years after Hijrah, my question is why do we always leave out the first 13 years of prophet hood before Hijrah. I know the year of Hijrah was a great year yet we all know that prophet hood started 13 years before this so when answering why don’t we mention this like now we are 1433 AH yet when answering why don’t we say Islam after prophet hood is 1446 adding the 13 years before the period. insha allah you can explain why we don’t add the first 13 years into our answer.

Addition Date: 2012-08-02

Short Link: http://IslamHouse.com/397556