Proleptic Gregorian calendar Julian and proleptic Gregorian calendar dates are as follows: The table below assumes a Julian leap day of 29 February, but the Julian leap day (the bissextile day) was in Latin or 24 February (see Julian reform), so dates between 24 and 29 February in all leap years were irregular. Note: When converting a date in a year which is leap in one calendar but not the other, include 29 February in the calculation when the conversion crosses the border between February and March. Proleptic Gregorian calendar The proleptic Gregorian calendar is produced by extending the Gregorian calendar backward to
Adoption of the Gregorian calendar the old style calendars were similar but not all the same. The Arabic numerals may be used for both calendar dates in modern Japanese and Korean languages, but not for Chinese old-style dates. Japan started using the Gregorian calendar on 1 January 1873, locally known as . The preceding day, 31 December 1872, was . Japan currently uses two eras: the western era and a modified traditional Japanese era name (nengō). The months and days are those of the Gregorian calendar, but the year is either the western year number or a year of the nengō of the emperor on