In the Gregorian calendar the date of the equinox of autumn happens on 21, 22, 23 or 24 September, in general on 22 or 23. It will return to fall on 21 only in 2092, and it will be the first time that this happens from the introduction of this calendar. It is verified on 24 instead in 1803, 1807, 1903, 1907, 1911, 1915, 1919, 1923, 1927 and 1931 and in the future in 2303!
www.pierpaoloricci.it/dati/autunno_eng.htm