Dear Jaime,

The answer  to   your   question is almost certainly, “no”. The Gregorian calendar was not implemented   until   February 24, 1582, so it  has  only  been in  operation  430  years–less than the length of time in your question.  Before it, we had the Julian calendar, which was similar, but used exactly 365.25 days per year, rather than the more accurate 365.2425 days per year of the Gregorian calendar. Nevertheless, people frequently project Gregorian calendar dates backward into history, even though they were not used at those times. However, this results in errors if, for example, you read an ancient document with a date of June 15, 1215 A.D., which is the Julian calendar, but fail to convert it to June 22 1215, the Gregorian dating system with which we are most familiar.

The exact length of a biblical year is an even more complex issue. The Jewish Rabbis have maintained a calendar from which they celebrate the Biblical Feast Days. The days of “Passover, “Rosh Hashanah” and “Yom Kippur” are typically printed as Jewish holidays on typical calendars of our day. However, nearly every scholar would agree that the calendar used by the Rabbis is not the same one used at the time of Christ or during the Old Testament. Today’s Rabbinical Calendar is calculated, whereas Jewish history records the ancient calendar was set by observing the moon and sun. Knowing exactly which “biblical” calendar was being used at any point in ancient history, or knowing exactly what the “true biblical calendar” should be, are questions of great debate.

Yes, there are many religious teachers who claim to have historical calendars worked out to know exact dates of multiple calendar systems throughout history. But these teachers do not all agree with each other. And every one of them will have either a set of rules that are not clearly commanded by scripture (they are “deduced from scripture”) or will  rely  on  some kind of governing  body  (even  if  it is themselves) to determine exactly when to start a new month or new year in certain situations. Such situations would include: How does one know when to begin a new month during cloudy weather when the moon is not visible? Should calculations be used instead? Should a new month begin when some people within a country or congregation can see the new moon but others cannot? (That happens when the new moon is barely visible). Do the majority of people need to see it or just the leaders? What should be done if the leaders cannot agree? In order to accept a sighting of a new moon, can the sun be anywhere? Or, does it all have to be below the horizon? Or, does it have to be so dark that stars are visible or even completely dark? There are more questions like these that the Bible does not directly answer. Yes, there are verses where one can draw inferences, but sincere teachers differ on their meaning.

You can learn a lot from my article, Biblical Calendar Basics on the Internet. While it explains calendar technicalities at length, it also shows the reason why some of this is not as important as we might think it is.

There are calendar conversion programs available, but I do not think these will completely solve your problem:

http://www.fourmilab.ch/documents/calendar

I am sorry that this took so long, but I think it was worth answering.