There are differences of opinion about how to determine the dates of the beginning of the year and the dates of the Lord’s commanded to keep holy days (for His set apart people). I’ve studied and, for now at least, this way of Scriptural understanding is what i believe. However, the dates (not the holy days) should not be a divisive issue.
How to calculate the calendar.
1) A year begins at the first new moon after the vernal equinox.
2) A month starts at the sundown after the lunar conjunction.
See our teachings “Calendar Confusion” and “The Calendar” to learn more.