converting the Gregorian calender to the Hijri calendar

The Islamic calendar is based on lunar cycles, so a month will begin with a crescent moon, and end with the next one. Because measuring a year in lunar cycles will give you only about 354 days, each month will shift across seasons. That is why Ramadan is celebrated at a slightly different time each year. The year zero in the Muslim Lunar Calendar corresponds to July 16, 622 CE. Why did Muslims choose to begin counting from this date? Is it the date that Muhammad (PBUH) was born, or perhaps the year he died? Is it night he was first visited by the angel Gabriel and told to recite the holy Qur'an? No. July 16, 622 CE is when Muhammad and a group of believers migrated to Medina (then called Yathrib) from Mecca. This is known as the Hijra, which is the Arabic word for migration. The reason for why this particular date was chosen is because it is when the early Muslims left the place where they had been persecuted for a town in which their ways of life would be respected and eventually copied. It is the first hint of the incredible power and influence that Islam will have in later centuries.

To convert a Gregorian date to a Hijri date follow this link: http://www.muslimphilosophy.com/ip/hijri.htm 

So according to the Hijri calendar we are in the year 1430. We would write this 1430 AH. AH stands for Anno Hijra, meaning in the year of the migration.

Lunde,Paul. Islam. New York: DK, 2002.