There is conclusive evidence to show that the prophetic year of Scripture is composed of 360 days, or twelve months of 30 days.
The first argument is historical. According to the Genesis record, the Flood began on the seventeenth day of the second month (7:11), and came to an end on the seventeenth day of the seventh month (8:4). Now, this is a period of exactly five months, and fortunately the length of the same period is given in terms of days-“an hundred and fifty days” (7:24; 8:3). Thus the earliest known month used in Biblical history was evidently thirty days in length, and twelve such months would give us a 360-day year.
The second argument is prophetical…Dan. 9:27 mentions a period of Jewish persecution….Since this persecution begins in the “midst” of the Seventieth Week and continues to the “end” of the Week, the period is obviously three and one-half years. Dan: 7:24-25 speaks of the same Roman Prince and the same persecution fixing the duration as “a time and times and the dividing of time”-in the Aramaic, three and a half times. Rev. 13:4-7 speaks of the same great political Ruler and his persecution of the Jewish “saints” lasting “forty and two months.” Rev. 12:13-14 refers to the same persecution, stating the duration in the exact terms of Dan. 7:25 as “a time and times and half a time”; and this period is further defined in Rev. 12:6 as ”a thousand two hundred and three score days.” Thus we have the same period of time variously stated as 3 ½ years, 42 months, or 1260 days. Therefore, it is clear that the length of the year in the Seventy Weeks prophecy is fixed by Scripture itself as exactly 360 days.(1)
The fact that this is the same as the three and one-half years, which in turn are equated with 1,260 days (Rev. 11:3; 12:6) and with 42 months (Rev. 11:2; 13:5), means that in Jewish reckoning each month has 30 days and each year 360 days. This confirms the 360-day Jewish year used in the calculations in the Correlation Chart.(2)
1). Things To Come by J. Dwight Pentecost p.243-244 (McClain).
2). Walvoord, John F. ; Zuck, Roy B. ; Dallas Theological Seminary: The Bible Knowledge Commentary : An Exposition of the Scriptures. Wheaton, IL : Victor Books, 1983-c1985, S. 1:1365
