I was looking for something like this, but couldn’t find an airtable formula so I thought I would share mine. This only covers the last 3 Japanese era’s.

I would be great if something like this could be added to the Set_Locales function for Japanese, but I didn’t see any others that changed the year numbers so it might not be possible.

Administratively I have deal with a lot of dates that need to passed to the local government and for birthdays we need to use the era years instead of the Gregorian years.

And if anyone has a better one please share.

IF(Birthday,SUBSTITUTE(SUBSTITUTE(IF(
    IS_BEFORE({Birthday},DATETIME_PARSE("Jan 8, 1989"))=1,"昭和"&(DATETIME_FORMAT({Birthday},"YYYY")-1925)&"年",
    
    IF(
        IS_BEFORE({Birthday},DATETIME_PARSE("May 1, 2019")),"平成"&(DATETIME_FORMAT({Birthday},"YYYY")-1988)&"年","令和"&(DATETIME_FORMAT({Birthday},"YYYY")-2018)&"年"))&DATETIME_FORMAT(Birthday,"M月D日"),"令和1年","令和元年"),"平成1年","平成元年"),BLANK())