How do you convert Japanese patent dates to Western calendar years?

This page is an FAQ based on guidance from the Manual of Patent Examining Procedure. It is provided as guidance, with links to the ground truth sources. This is information only: it is not legal advice.

Converting Japanese patent dates to Western calendar years involves a simple calculation based on the year of the Emperor’s reign. The MPEP 901.05(a) provides specific instructions:

“To convert the Japanese year of the Emperor to the Western calendar year, for years prior to 1989, add 1925 to the JAPANESE YEAR. For example: 40.3.6 = March 6, 1965. For years after 1988, add 1988 to the JAPANESE YEAR.”

So, for dates before 1989, add 1925 to the Japanese year. For dates from 1989 onwards, add 1988 to the Japanese year.