Agreement of the dates of the calendars republican and Gregorian

The year I began the September 22nd 1792 and finished the September 21st 1793.

The Jour sextile (sixth epagomene day) was given in republican end of the year preceding the years multiple by four. Consequently, between the 1st Vendémiaire of the year IV (September 23rd 1795) and the February 29th 1796 (10 Ventôse of the year IV) the correspondence is shifted one day. It is necessary to add one day to the day of the Gregorian calendar or to withdraw one day at the day of the republican calendar.

To this shift the fact is added that the year VIII was bissextile whereas the year 1800 was not it. Consequently, starting from March 1st 1800 (10 Ventôse of the year VIII) there is shift of new a Jour between the two calendars (in the same direction).

To convert a Gregorian date into republican date

  • To withdraw 1792 at the Gregorian year.
  • If the Gregorian date is posterior with the September 22nd (included), to add one year to the previous year.
  • To carry out conversion in the list, one must obtain a republican date then. It is perhaps not yet the good one, this republican date will be referred thereafter under the name “dates temporary” .
  • If the republican year is multiple of 4 and that the date of origination does not lie between on March 1st and the September 21st (included), to withdraw one day at the republican temporary date (possibly by changing republican year if need be).
  • If the date of origination is posterior at March 1st 1800 (included), to still withdraw a day at the republican temporary date.

Example: the September 22nd 1803

  • 1803-1792 = 11
  • the date is posterior with the September 22nd (included), one adds 1 to the year, one thus finds 12.
  • the September 22nd corresponds to the 1 Vendémiaire. The temporary date is the 1 Vendémiaire of year XII.
  • the republican year is multiple of 4, and moreover the date of origination is not included/understood between on March 1st and the September 21st: one thus withdraws a day at the temporary date which becomes the Jour of the revolution of year XI.
  • As the date is posterior at March 1st 1800, the true republican date is still the day before: the Day of the rewards of the year XI .

To convert a republican date into Gregorian date

  • To add 1792 to the republican year.
  • If the date lies between the 1 Vendémiaire and the 11 Nivôse (included), to withdraw one at the year previously calculated.
  • To carry out conversion in the list, one must obtain a Gregorian date then. It is perhaps not yet the good one, this Gregorian date will be referred thereafter under the name “dates temporary” .
  • If the republican year of origin is multiple of 4 and that the date lies between the 1st Vendémiaire and the 11 Nivôse (included), to add one day to the Gregorian temporary date.
  • If the temporary date is posterior with the February 28th 1800 (excluded), to still add a day to the Gregorian temporary date.

Example: the Day of the rewards of the year XI.

Table of correspondence

the correspondence of the dates is given as an indication. Indeed they slightly varied from one year to another. See the articles Year I with Year XIV for the exact correspondences.

See too

External bonds

  • Software of date conversion

  • Date conversion into line
  • Summary table of agreement

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