Since Elizabeth (John’s mother) was in her sixth month of pregnancy when Jesus was conceived (Luke 1:24-36), we can determine the approximate time of year Jesus was born if we know when John was born. John’s father, Zacharias, was a priest serving in the Jerusalem temple during the course of Abijah (Luke 1:5). Historical calculations indicate this course of service corresponded to June 13-19 in that year.
It was during this time of temple service that Zacharias learned that he and his wife Elizabeth would have a child (Luke 1:8-13). After he completed his service and traveled home, Elizabeth conceived (Luke 1:23-24). Assuming John’s conception took place near the end of June, adding nine months brings us to the end of March as the most likely time for John’s birth. Adding another six months (the difference in ages between John and Jesus) brings us to the end of September as the likely time of Jesus’ birth.