Also called the French Republican Calendar, its particularity is to be divided in 12 months of exactly 30 days, and each month in 3 weeks of 10 days. The beginning of the year was the Autumnal Equinox (around 22 September).

It was designed during the French Revolution and used between 1793 and 1805. It was finally abolished by Napoleon, soon after his coronation as emperor.

The Republican calendar year began at the autumn equinox and had twelve months of 30 days each, which were given new names based on nature:

* Autumn:
o Vendémiaire (from Latin vindemia, "vintage") Starting Sept 22, 23 or 24
o Brumaire (from French brume, "mist") Starting Oct 22, 23 or 24
o Frimaire (From Latin frimas, "frost") Starting Nov 21, 22 or 23
* Winter:
o Nivôse (from Latin nivosus, "snowy") Starting Dec 21, 22 or 23
o Pluviôse (from Latin pluviosus, "rainy") Starting Jan 20, 21 or 22
o Ventôse (from Latin ventosus, "windy") Starting Feb 19, 20 or 21
* Spring:
o Germinal (from Latin germen, "seed") Starting Mar 20 or 21
o Floréal (from Latin flos, "flower") Starting Apr 20 or 21
o Prairial (from French prairie, "meadow") Starting May 20 or 21
* Summer:
o Messidor (from Latin messis, "harvest") Starting Jun 19 or 20
o Thermidor (from Greek thermos, "hot") Starting Jul 19 or 20
o Fructidor (from Latin fructus, "fruits") Starting Aug 18 or 19

The month is divided into three decades or 'weeks' of ten days each, named simply:

* primidi (first day)
* duodi (second day)
* tridi (third day)
* quartidi (fourth day)
* quintidi (fifth day)
* sextidi (sixth day)
* septidi (seventh day)
* octidi (eighth day)
* nonidi (ninth day)
* décadi (tenth day)

Each day was given the name of a plant or flower to replace the Catholic "saints' days".

In an attempt to simplify and rationalise the newly founded metric system (officially adopted in 1791), a decimal time system was created in 1793. Each day was divided into ten hours, each hour into 100 decimal minutes and each decimal minute had 100 decimal seconds. However decimal time didn't catch on and was quickly abandoned in 1795.

One of the purpose of the calendar was to do away with the system of the old monarchist regime. However, the Gregorian calendar we use nowadays was in fact a variant of the Julian calendar designed by Julius Caesar. So it is rather surprising that the neo-classical "Rome-enthusiasts" of the French Revolution should abolish a Roman-style calendar. Maybe this is also why Napoleon abolished it after being crowned emperor in Rome.

N.B. : Today is the 7th day of the first week of Vendemiaire, year 215.