I haven't seen any number crunching for a while so I am giving it a go for the upcoming fall Jewish holy days. Daniel 9:27 is initially where the idea of a 7 year tribulation comes from, one week represents a week of years, 7 years. According to Daniel 12:11, the second half of the week contains an extra month. Jewish years are 360 day years, so 7 years is 360 X 7 = 2520. The seven years can be split in half which is 1260 + 1260, with the extra month added on the second half it becomes 1260 + 1290 which equals 2550 days for the tribulation period
"Daniel 9:27 King James Version (KJV)27 And he shall confirm the covenant with many for one week: and in the midst of the week he shall cause the sacrifice and the oblation to cease, and for the overspreading of abominations he shall make it desolate, even until the consummation, and that determined shall be poured upon the desolate."
"Daniel 12:11 King James Version (KJV)11 And from the time that the daily sacrifice shall be taken away, and the abomination that maketh desolate set up, there shall be a thousand two hundred and ninety days."
From the last or seventh day of Sukkot (Feast of Tabernacles) this year, 2018, until Rosh Hashanah of 2025 it is exactly 2550 days. Not sure if it means anything or is just an interesting anomaly.
Calculation from timeanddate.com:
From Sunday, September 30, 2018
Added 2550 days
Result: Tuesday, September 23, 2025
REFERENCE: 2018 holidays
Holiday Dates Description Rosh Hashana Sep 10-11, 2018 M‑Tu The Jewish New Year Yom Kippur Sep 19, 2018 W Day of Atonement Sukkot
Sep 26-30, 2018 W‑Su
Feast of Tabernacles
REFERENCE: 2025 holidays
Rosh Hashana Sep 23-24 Tu‑W The Jewish New Year Yom Kippur Oct 2 Th Day of Atonement Sukkot Oct 7-8 Tu‑W
Oct 9-13 Th‑MFeast of Tabernacles