The enthronement date of Emperor Jimmu has been considered to have been determined on the basis of the description in Nihonshoki to be New Year's Day (of the old calendar) or February 11th (of the new calendar) in 660 B.C. legally and conventionally since the Meiji period.
神武天皇の即位年月日は、『日本書紀』の記述に基づいて、明治以来、法的・慣習的に紀元前660年の旧暦元旦、新暦の2月11日とされている。