What is the difference between the Christian and the Jewish calculation of Anno Mundi?

What is the difference between the Christian and the Jewish calculation of Anno Mundi?

There are many differences differences between the literalist Christian and Jewish calculations of Anno Mundi. There are equally various different calculations and historical interpretations within each of these individual manners of calculations also. In a simple word the whole affair is complicated.

The best person who has explained the various differences between these two Anno Mundi calculations and the divergences within each of these calendars is Matt Baker who has a PhD in Psychology of Religion. It is excellently explained in his YouTube video: Jewish Calendar vs Christian Literalists | Biblical Chronology Explained

I will somehow try to explain these differences as best I can. These differences are multi faceted and historical data at times is simply second guess at best.

To start off with the Jewish calculations take the point of departure to be scheme of 4,000 years taking the re-dedication of the Temple by the Maccabees in 164 BCE as its end-point.

Many Literalist Christians take the end point to be the Birth of Christ, but not all.

The early Church Father Eusebius (c. 260–340), attempting to place Christ in the chronology, put his birth in AM 5199, and this became the accepted date for the Western Church. As the year AM 6000 (800 CE) approached there was increasing fear that the end of the world was nigh, until the Venerable Bede made his own calculations and found that Christ's birth took place in AM 3592, allowing several more centuries to the end of time.

Martin Luther (1483–1546) switched the point of focus from Christ's birth to the Apostolic Council of Acts 15, which he placed in the year AM 4000, believing this marked the moment when the Mosaic Law was abolished and the new age of grace began. This was widely accepted among European Protestants, but in the English-speaking world, Archbishop James Ussher (1581–1656) calculated a date of 4004 BCE for creation; he was not the first to reach this result, but his chronology was so detailed that his dates were incorporated into the margins of English Bibles for the next two hundred years. This popular 4,000 year theological timespan, which ends with the birth of Jesus, differs from the 4,000 timespan later proposed for the Masoretic text alone, which ends with the Temple rededication in 164 BCE. - Chronology of the Bible

Another influential point between these calculations is that the Jewish calculations use the Masoretic Text, while other calculations are influenced by the other chronologies such as the Septuagint, Samaritan, Jubilees and Seder Olam.

When comparing an AD date to an AM date, we should subtract a year from the AD count because there is no “0 year”. Notice there are only 33 years between 4BC and 30AD.

Modern Christian literalists now seem to follow the Septuagint, while the Jewish calculations are based on the Hebrew Bible.

The canonical text of the Hebrew Bible is called the Masoretic Text, a text preserved by Jewish rabbis from early in the 7th and 10th centuries CE. There are, however, two other major texts, the Septuagint and the Samaritan Pentateuch. The Septuagint is a Koine Greek translation of the original biblical Hebrew holy books. It is estimated that the first five books of the Septuagint, known as the Torah or Pentateuch, were translated in the mid-3rd century BCE and the remaining texts were translated in the 2nd century BCE. It mostly agrees with the Masoretic Text, but not in its chronology. The Samaritan text is the text preserved by the Samaritan community. This community dates from some time in the last few centuries BCE—just when is disputed—and, like the Septuagint, differs markedly from the Masoretic Text in its chronology. Modern scholars do not regard the Masoretic Text as superior to the other two—the Masoretic is sometimes clearly wrong, as when it says that Saul began to reign at one year of age and reigned for two years. More relevantly, all three texts have a clear purpose, which is not to record history so much as to bring the narrative to a point which represents the culmination of history.

In the Samaritan Pentateuch, the genealogies and narratives were shaped to ensure a chronology of 3000 years from creation to the Israelite settlement of Canaan. Northcote reports this as the "Proto-SP chronology," as designated by John Skinner (1910), and he speculates that this chronology may have been extended to put the rebuilding of the Second Temple at an even AM 3900, after three 1,300-year phases. In the Septuagint version of the Pentateuch the Israelite chronology extends 4,777 years from creation to the finishing of the Second Temple, as witnessed in the Codex Alexandrinus manuscript. This calculation only emerges by supplementing Septuagint with the MT's chronology of kings. There were at least 3 variations of Septuagint chronology; Eusebius used one variation, now favored by Hughes and others. Northcote asserts that the Septuagint calendrical pattern was meant to demonstrate that there were 5,000 years from creation to a contemporaneous Ptolemaic Egypt, circa 300 BCE.

The 2nd century BCE Book of Jubilees begins with the Creation and measures time in years, "weeks" of years (groups of seven years), and jubilees (sevens of sevens), so that the interval from Creation to the settlement of Canaan, for example, is exactly fifty jubilees (2450 years).

Dating from the 2nd century CE, and still in common use among Jews, was the Seder Olam Rabbah ("Great Order of the World"), a work tracing the history of the world and the Jews from Creation to the 2nd century CE. It allows 410 years for the duration of the First Temple, 70 years from its destruction to the Second Temple, and 420 years for the duration of the Second Temple, making a total of 900 years for the two temples. This schematic approach to numbers accounts for its most remarkable feature, the fact that it shortens the entire Persian Empire from over two centuries to just 52 years, mirroring the 52 years it gives to the Babylonian exile. -Other chronologies: Septuagint, Samaritan, Jubilees, Seder Olam

According to classical Jewish sources, the Hebrew year 6000 (from sunset of 29 September 2239 until nightfall of 16 September 2240 on the Gregorian calendar) marks the latest time for the initiation of the Messianic Age. The Talmud, Midrash, and the Kabbalistic work, the Zohar, state that the date by which the Messiah must appear is 6,000 years from creation. According to tradition, the Hebrew calendar started at the time of Creation, placed at 3761 BCE. The current (2021/2022) Hebrew year is 5782. - Year 6000

After explaining the background, Dr. Matt Baker asks (at 20:28): "Which one of the chronologies is the correct one?" and answers: "In my opinion, the obvious answer is: none of them." He then brings up David Rohl's recent Patterns of Evidence, but dismisses it as against current consensus of Egyptologists. In the end it is impossible to know which literalistic chronology is the correct one as some biblical historical dated events can not be definitively ascertained!

Many external influences will remain hidden to our modern eyes for any one A.M. Chronology to be acceptable to most of us, whether literalists or not.