How many days and weeks are there in the Jewish/Biblical year? Also, is there a current Jewish calendar that is different from the biblical one, and if so, how many days and weeks are there in that calendar?
The original calendar as God ordained it had 12 thirty day months for a 360 day year. In about 701 BC something happened that caused the year to be lengthened to 365.25 days, although scholars have discovered that God has always used the 360 day year when calculating dates in prophecy. That’s how the 3 1/2 year-long Great Tribulation can also be 42 months and 1260 days long.
Sometime after 701 BC, months on the Hebrew calendar became either 29 or 30 days, corresponding to the 29 1/2-day lunar cycle. The problem is that lunar years are approximately 12.4 lunar months long, so a 12-month lunar calendar loses about 11 days every year. To compensate for this drift, a 13th month was occasionally added to realign the months with the seasons.
In the fourth century, Hillel II established a fixed calendar based on mathematical and astronomical calculations. This calendar, still in use, standardized the length of months and the addition of months over the course of a 19 year cycle, so that the lunar calendar realigns with the solar years. The extra month is now added in the 3rd, 6th, 8th, 11th, 14th, 17th and 19th years of the cycle. The current 19 year cycle began on October 12, 1997.
So in a regular Jewish year, there are usually 355 days and in a leap year there are 384. Their weeks have 7 days like ours so there are 50.7 weeks in a regular year and 54.8 in a leap year.