Modern French coins use the Gregorian calendar, but the French Republican Calendar (RE) was used on "Napoleons" (20 franc gold coins) between 1803 and 1806. The French Republican Calendar starts on September 22, 1792 and increases by one year every autumnal equinox. The years were denoted by the letters "AN" (French for "year") followed by Roman or Arabic numerals. See the examples below.

Date RE AD
AN XI RE1 September 24, 1803 - September 23, 1804
AN 12 RE4 September 23, 1804 - September 23, 1805
AN 13 RE13 September 23, 1805 - September 23, 1806
AN 14 RE13 September 23, 1806 - September 23, 1807