Occasionally when I am studying Daniel and Revelation with someone, they will question how we get 360 days to a prophetic year instead of 365. The story of Noah actually confirms for us that in Bible times each month had exactly 30 days, thus giving us 360 years in a Bible year. 

First, where do we get a day for a year in Bible prophecy? 

While I don’t know that this is necessarily appointing a day for a year in Bible prophecy, I find it interesting that when Laban tells Jacob to work seven more years for Rachel, he calls it a week. That would be a day for a year. 

Fulfill her week, and we will give you this one also for the service which you will serve with me still another seven years. Genesis 29:27 NKJV

The first time we find a day for a  specific year in prophecy is in Numbers 14:34,

According to the number of the days in which you spied out the land, forty days, for each day you shall bear your guilt one year, namely forty years, and you shall know My rejection.

Later, in Ezekiel 4:5-6 this year/day principle is repeated. 

For I have laid on you the years of their iniquity, according to the number of the days, three hundred and ninety days; so you shall bear the iniquity of the house of Israel.  And when you have completed them, lie again on your right side; then you shall bear the iniquity of the house of Judah forty days. I have laid on you a day for each year.

So now, how does the story of Noah and the flood help us establish one year equaling 360 days to a year in Bible prophecy?

In the six hundredth year of Noah’s life, in the second month, the seventeenth day of the month, on that day all the fountains of the great deep were broken up, and the windows of heaven were opened. Genesis 7:11NKJV

And the waters prevailed on the earth one hundred and fifty days. Genesis 7:24 NKJV

And the waters receded continually from the earth. At the end of the hundred and fifty days the waters decreased. Then the ark rested in the seventh month, the seventeenth day of the month, on the mountains of Ararat. Genesis 8:3-4 NKJV

Here we see clearly that from the 17th day of the second month to the 17th day of the seventh month is exactly 150 days. Every month had 30 days equaling 360 days for a hear. With this in mind, the 42 months of Revelation 13:5 would be 1260 prophetic days or 1260 years. 

You may study this week’s Sabbath School lesson here.