Days, Weeks, Months and Years


From the start the Bible has given us both a way to describe a day and the terms of it. "In the beginning, God created the heavens and the earth. The earth was without form and void, and darkness was over the face of the deep. And the Spirit of God was hovering over the face of the waters. And God said, ‘Let there be light’, and there was light. And God saw that the light was good. And God separated the light from the darkness. God called the light Day, and the darkness he called Night. And there was evening and there was morning, the first day." (Gen.1:1‑5 English Standard Version)

The terms are given for the seasons or cycles of a year. "God said, ‘Let there be lights in the expanse of the heavens to separate the day from the night. And let them be for signs and for seasons, and for days and years, and let them be lights in the expanse of the heavens to give light upon the earth.’ And it was so. And God made the two great lights—the greater light to rule the day and the lesser light to rule the night—and the stars." (Gen.1:14‑16 ESV).


The account of the flood or story of the deluge uses days and months in a year to describe when it began and when it ended. "In the six hundredth year of Noah’s life, in the second month, on the seventeenth day of the month, on that day all the fountains of the great deep burst forth, and the windows of the heavens were opened. And rain fell upon the earth for forty days and forty nights….The fountains of the deep and the windows of the heavens were closed, the rain from the heavens was restrained, and the waters receded from the earth continually. At the end of 150 days the waters had abated.and in the seventh month, on the seventeenth day of the month, the ark came to rest on the mountains of Ararat." (Gen.7:11‑12, Gen.8:2‑4 ESV). This shows five months and therefore that each month was 30 days long. This was consistent with the Sumerian Calendar of the years prior to 1500 B.C.


The Julian Calendar introduced by Julius Caesar fixed a year to be 365¼ days. However this was not entirely correct which lead to the Gregorian Calendar of 1582, which showed a solar year was 365 days. 5 hours. 49 minutes and 12 seconds. A solar month is 30 days. 10 hours. 29 minutes and 4.1 seconds.

Lunar Calendar

However the Bible uses the moon to calculate the first month and length of a month. A lunar month is 29 days. 12 hours. 44 minutes and 2.87 seconds. It therefore follows that 12 lunar months are only 354 days. 8 hours 48 minutes and 34 seconds.

For Israel the phases of the moon were used to set the time of the festivals starting with the Passover and the exact days that certain things had to be done. The Heavenly Father used signs that they could readily use to set the months of the year, such as the Spring Equinox. Therefore the first month of the spiritual year starts with the first new moon. The direction for this was given in Exod.12:2 (ESV) when Nisan was allocated the first month of the year "This month shall be for you the beginning of months. It shall be the first month of the year for you."

The Spring Equinox is when in springtime in the northern hemisphere night and day are the same length. Pears Encyclopaedia describes the Equinox as when "the sun crosses the plane of earth’s equator". It occurred with the ripening of the barley and the flax but before the wheat was ripe. Therefore it provided Israel with a clear sign at which to begin the year with the cycle of the moon for the first month. In this way unlike a British calendar with 12 months there would sometimes be thirteen months in a Jewish year which was called an "Intercalary Month". Just as the Passover on the 14th Nisan, Easter and Greek Easter are calculated using the Lunar Calendar. Knowing this it is easier to understand why these dates vary from year to year. Whereas the Spring Equinox is either the 20th or 21st March each year in the Gregorian Calendar.

Israel was not alone in using this Lunar Calendar. At this time the Babylonians used this type of calendar starting with their month named Nisanu for the first month Nisan. They also called the Jewish month of Tishri, Tashritu and Adar, Addaru and so on.

Day‑Year Principle

The book of Daniel used weeks to prophesy when certain events would take place. It describes the significant Seventy Weeks in Daniel 9:24‑27."Seventy weeks are decreed about your people and your holy city, to finish the transgression, to put an end to sin, and to atone for iniquity, to bring in everlasting righteousness, to seal both vision and prophet, and to anoint a (the) most holy place. Know therefore and understand that from the going out of the word to restore and (re)build Jerusalem to the coming of an anointed one, a prince, there shall be seven weeks. Then for sixty‑two weeks it shall be built again with squares and moat, but in a troubled time. And after the sixty‑two weeks, an anointed one shall be cut off and shall have nothing. And the people of the prince who is to come shall destroy the city and the sanctuary. Its end shall come with a flood, and to the end there shall be war. Desolations are decreed. And he shall make a strong covenant with many for one week, and for half of the week he shall put an end to sacrifice and offering. And on the wing of abominations shall come one who makes desolate, until the decreed end is poured out on the desolator." (ESV)

It states when the Messiah, the prince, the Anointed one would come and that he would be cut off in the middle of the week. The Hebrew word shabua translated week, which is Strong’s word 7620 and literally means ‘sevened’. Counting would begin from the command to restore and build Jerusalem in 454 B.C. and therefore would end in 37 A.D. One thought was that the initial 7 weeks or 49 years represent the time it took to rebuild the city. This uses the day for a year calculation, sometimes described the "Day‑Year Principle" described in Numbers 14:34 and Ezekiel 4:6.

The same formula is often applied to the 3½ years that are mentioned in the Bible. This occurs in 3 main forms, as follows;

1,260 days – Rev.11:3; Rev.12:6.

42 months – Rev.11:2; Rev.13:5.

Time, times and a half – Dan 7:25; Dan.12:7; Rev.12:14.

Prophetic Year

This works with the idea that a month is 30 days and as 42 multiplied by 30 is 1,260 then a year must be reckoned as 360 days long, a so‑called prophetic year of 360 days.

If a 360 day calendar was used, a bridge was needed to account for the solar year being 365 days long. This was done at the end of the year by adding 5 non‑days and presumably 6 non‑days for a leap year.

If one takes a glance at a lunar year of about 354 days and a solar year about 365 days then it also seems reasonable to work with a year of 360 days. Our Lord Jesus’ ministry was 3½ literal years or half a week which places the start of his ministry around the time of the Day of Atonement or Feast of Tabernacles which takes place on 15th Tishri, the seventh month of the Hebrew Calendar.

What is the point of all this? God is working to a pattern and there is a code that can be used. The Day‑Year Principle that works accurately for the prophecy in Daniel has been used by a number of students of the Bible for the probable date of the Second Advent or the end of this world‑age as have other methods. This helps to understand what the Bible states about calculating time when the calendar is quite different from the one we use here in the U.K.

Readers may wish to know that 14th Nisan in 2019 starts at 6 p.m. on Thursday 18th April.

N.B. ESV = English Standard Version