The Feast Days:
Feast of Trumpets: 16 September (begins sundown 15 September)
Day of Atonement: 25 September (begins sundown 24 September)
Feast of Tabernacles: 30 September (begins sundown 29 September)
through (day eight) ending 7 October (at sundown).
Leviticus 23:23 And the "I AM" spoke unto Moses, saying,
23:24 Speak unto the children of Israel, saying, In the seventh month, in the first [day] of the month, shall ye have a Sabbath, a memorial of blowing of trumpets, an holy convocation.
23:26 And the "I AM" spoke unto Moses, saying,
23:27 Also on the tenth [day] of this seventh month [there shall be] a Day of Atonement: it shall be an holy convocation unto you; and ye shall afflict your souls, and offer an offering made by fire unto the "I AM".
23:28 And ye shall do no work in that same day: for it [is] a Day of Atonement, to make an atonement for you before the "I AM" your God.
23:32 It [shall be] unto you a Sabbath of rest, and ye shall afflict your souls: in the ninth [day] of the month at evening, from evening unto evening, shall ye celebrate your Sabbath.
23:33 And the "I AM" spoke unto Moses, saying,
23:34 Speak unto the children of Israel, saying, The fifteenth day of this seventh month [shall be] the Feast of Tabernacles [for] seven days unto the "I AM".
23:35 On the first day [shall be] an holy convocation: ye shall do no servile work [therein].
23:36 Seven days ye shall offer an offering made by fire unto the "I AM": on the eighth day shall be an holy convocation unto you; and ye shall offer an offering made by fire unto the "I AM": it [is] a solemn assembly; [and] ye shall do no servile work [therein].
23:39 Also in the fifteenth day of the seventh month, when ye have gathered in the fruit of the land, ye shall keep a feast unto the "I AM" seven days: on the first day [shall be] a Sabbath, and on the eighth day [shall be] a Sabbath.
23:44 And Moses declared unto the children of Israel the Feasts of the "I AM". King of kings' Bible - Leviticus
Hannah Michaels explains further: