The Hijri lunar dating system is the second-most used calendar after the Common Era or Gregorian calendar. Established with the first year corresponding to the year 622 CE (Common Era or AD), it is set to represent the year the prophet Muhammad, and his followers migrated from Mecca to Medina. This event, known as Hijra, is where the use of AH for “Anno Hegirae” or “in the year of Hijra” originates.
This lunar calendar is based on the cycles of the moon, with 12 lunar months and a year of 354 or 355 days. Because of this, direct conversion from AH coin dating to a CE coin date cannot be 100% accurate and is often estimated. Usually, the conversion is the AH date plus 622, which is usually accurate to within a year.
The AH coin dating system is found on coins of countries all over the world from Morocco to China. Complicating the conversion of the dating system for some countries, the additional information of a regnal year (a year designated by a king or his reign) has been added to some issues. This year represents the current year that the ruler has been in power. In addition to this, some coins are issued with a frozen AH year, and only the regnal year changes. These coins can still easily be converted to Common Era dating by simply adding the regnal year to the frozen Hijri date and adding 622. For most countries, modern coinage that still uses a Hijri date has an additional Common Era date added to the coins.
We at PCGS have worked hard over the last few years to update our system to add the additional coin dates on the label website information. For coins that have an AH date, we will note the AH date and the Common Era date conversion, for example, AH1322 (1904). With coins that have the additional regnal year, we will label them AH1223//21 (1827). With coins bearing joint dates, we will label them as AH1348-1929.