Analysis of lunar cycles yields ideal times between March 18 and April 18 for the Passover in the first century. However, the calendar could be off by up to three days relative to the moon. Therefore, the limits have been extended by three days to yield March 15 to April 21.

Analysis of the Elephantine papyri from the 5th century BC show that the earliest passover occurred as early as March 11 in the year 460 BC. The following elephantine papyri supports this fact based on a date of November 11, 460 BC for the Hebrew calendar date of Kislev 2.

Since Kislev is the 9th month in the Hebrew calendar, we must subtract 9 lunar cycles to arrive at a Nisan 1 date as early as February 26 or February 27, 460 BC. The Passover lamb would have been slain on March 11 or March 12, 460 BC.

It is important to understand that we have counted back from the Hebrew month Kislev instead of forward. There would not have been any leap month to be inserted between the month of Nisan to the month of Kislev.

Additional support for this early passover date comes from comparing how the Hebrew months align to the Egyptian months in the Elephantine papyri. A Hebrew calendar is shown to range a minimum of 42 days relative to the Egyptian calendar.

Astronomical evidence based on the 5th century BC papyri from Elephantine, Egypt support that the earliest Passover occurred about March 11 in the 5th century BC.