As the New Year approaches, I start to be aware that I have to change the year number on the dates of my calligraphies. I’ll be one of those people who’ll still write 2016 well into the middle of January. So I have to make a conscious effort to make sure I’m writing the correct year.
I don’t always date my calligraphies in Japanese, but when I do, I like to use the traditional Japanese Era Years. Of course, if you date your calligraphy you can remember when the calligraphy was brushed and this can add some value to it. However, dating the calligraphy, meaning brushing the date in Kanji, can also add to the visual aesthetics of the piece. Dates are often brushed in small lettering on the left hand side of the calligraphy and/or above the signature.
I always keep the Japanese current era year written somewhere on my dry erase board so I don’t forget it.
Era years?
Yes, the Japanese keep track of their years based on the emperor in power.
The current era in Japan is called REIWA. The REIWA era began in May 1st, 2019 when the current emperor, Naruhito, took the throne.
The previous era, HEISEI, was from January 1989 until April 2019. Therefore, 1989 is considered HEISEI 1. Prior to HEISEI the era was known as SHOWA. The SHOWA era corresponds to the reign of Emperor Hirohito which lasted from 1926-1989. As an example the year I was born, 1981, is known as SHOWA 56. Before SHOWA was TAISHO and before that was MEIJI and so on. 
The Era is then followed by the year number. The Kanji for year is 年 and it is pronounced NEN. It is common to simply write the year number in roman letters or Kanji followed by NEN. Ex. 2016年 or 二０一六年.
Brushing the date using the Era is a bit more complicated, and longer, but I think it looks better in calligraphy. The Kanji for HEISEI 平成 particularly look beautiful when brushed in Gyosho and Sosho.
To write the date in the traditional way write first HEISEI, followed by the number, followed by NEN 年.
Example:平成二十九年 – HEISEI NIJUUKYUU NEN – HEISEI 2017 YEAR.