On Japanese coins, the date is recorded by writing the name of the emperor and the year of his reign. On Japanese coins, the date consists of four to six characters that is divided into three different sections. The first two characters, which can be in any order, is the name of the Emperor. The next one to three characters is the year of the Emperor's reign. The last character is the word year. You will need to be able to recognise some basic Japanese symbols in order to calculate the date.
If there are a number of symbols on the coin, look for the Japanese symbol for year which is "nen." This will always be the last character in the date.
Look at the first two characters to determine the name of the reign era, this is known as the "nengo." Remember, the characters can be in any order. Coins from 1989 are from the Heisei era. Coins dated between 1926 and 1989 are from the Showa era. The Taisho era puts the coin between 1912 and 1926. The Meiji era was from 1868 until 1912.
Look at the characters between the reign era and the word year. This may be in Roman numerals or in Japanese numbers. If it is in Roman, skip to Step 6.
Count the number of characters. If there are four characters means that the coin was made in the first ten years of the emperor's reign. Five characters indicates that the coin was made between the 11th and 19th years of the emperor's reign. Three characters indicates that the year of reign is above 20. The first year of an emperor's reign is called "gannen" and not labelled as year 1.
If the date has three characters, multiply the first character by the second character (the symbol for 10) and add the third character. For example, if the characters translate into 2 10 1, it indicates the 21st year.
Once you have the name of the reign era and the era year, use it to translate it into Western years. You can also do this manually by finding out when the years the emperor reigned. Step 2 listed the dates for the most current eras.