How many days in September 2031?

30 days

September 2031 runs from Monday the 1st to Tuesday the 30th.

Calendar grid for 9/2031, weeks starting Sun
ISO week	Sun	Mon	Tue	Wed	Thu	Fri	Sat
36	31	1Labor Day	2	3	4	5	6
37	7National Grandparents Day	8	9	10	11Patriot Day	12	13
38	14	15	16	17	18Rosh Hashanah	19	20
39	21	22	23Mabon	24	25	26	27Yom Kippur
40	28	29	30	1	2	3	4

About September 2031

September 2031 has 30 days, of which 22 are weekdays and 8 fall at the weekend. Taking out the 1 federal holiday leaves 21 working days.