I have interpreted Luke 2:6, “And it happened in their being there, the days were fulfilled for her to give birth” as referring to the standard term of days from conception to birth (38 weeks, 266 days) or from the start of the last cycle to birth at 280 days, which is 14 days more since conception averages on the 14th day of the cycle. Thus 280-14 = 266. Now it may be supposed by some who wish to escape from the conclusion that it refers to a definite term of days that it refers to a vague or indefinite time to give birth. We will do this first by investigating the other uses by Luke of the key phrase “the days were fulfilled,” and see if it refers to a definite term of days. Then we will know what is probable in the case of Luke 2:6.
The first use by Luke of the phrase in Luke 1:23, “And it happened, as were fulfilled the days of his service, he went to his house.” The days of Aνıyah’s service were exactly one week, from noon on the Sabbath July 6th to noon on the Sabbath July 13th. The priestly divisions served for one week each. So we see here that Luke means a definite number of days in his use of days being fulfilled.
I should probably pass over Luke 1:57 as the word “time” is used instead of days, “ἐπλήσθη ὁ χρόνος,” but the meaning is probably the same as those phrases with days and fulfilled since the context is giving birth. This means her term was complete. We see the same use of the words time and fulfilled in Mark 1:15 John 7:8 and Rev. 6:11. It is likely in the plan of the Almĭghty that a definite time was assigned for each, but it may not have been planned to an exact number of days in every case. In the case of John 7:8, the exact date of Messiah death was indeed planned out in advance. In the case of Elıshaνa, “καὶ ἐγέννησεν υἱόν” = “Then she gave birth to a son,” the implication of the text is that she did not go past the due date. So she have birth on II.1, 2 BC (April 5-6). The immediacy of the suggested waw consecutive for a Hebrew version and the parallel case of Messiah strongly suggest that the birth was on the due date.
The second phrase involving “days” and “fulfilled” is Luke 2:6. Now if we consider the fact Zeƙaryah arrived at home on V.1 (July 14th, 3 BC), and that six months later, on the first day of the sixth month of Elıshaνa (X.1, Dec. 10, 3 BC) the announcement was made to Miryam, then we see that the exact term of days remain to Tishri 1, 2 BC, i.e. 266 from conception to birth. It would seem probable based on a study of preferred dates for prophetic visions that the first day of a month is favored. Following this likelihood, then Luke 2:6 works out to 266 days. So we see that the likelihood that it was the first day of the sixth month points to an exact term, and an exact term means that Luke 2:6 alone likely refers to an exact term.
In the third case Luke says in 2:21, “And when eight days were fulfilled to circumcise the child then his name was called Yeshua.” We see here that days being fulfilled refers to a definite number of days.
In Luke 2:22 follows another use, “And when the days of their purification were fulfilled, according to the law of Moshe, they brought him up to Yerushalayim to present to Yăhwɛh.” Now the Torah ordains that there shall be 33 days of purification for a male child from the day of circumcision onward (cf. Lev. 12:1-4). We see again that the use of the words days and fulfilled refers to a definite number of days fixed beforehand.
In Acts 9:23, Luke states, “As yet were fulfilled sufficient days....” Here he qualifies the phrase with “sufficient,” or “considerable” (ἱκαναί). The extra word makes it clear that the phrase is not an exact number of days predetermined, but only so many days as needed for events to transpire.
Going outside of Luke we have another prophetic birth in Gen. 25:24. The evidence here also implies a birth on the term date, “καὶ ἐπληρώθησαν αἱ ἡμέραι τοῦ τεκεῖν αὐτήν καὶ τῇδε ἦν δίδυμα ἐν τῇ κοιλίᾳ αὐτῆς” = “And were fulfilled the days for her to give birth, and here there were twins in her womb.” The Hebrew reads likewise, “וְהִנֵּה תוֹמִם” = “and behold twins.” The abruptness of the phrase suggests that the birth was at the term date and not past it.
In Gen. 29:21, Ya‘aqoν says his days were fulfilled. Since he and his uncle had agreed on a set number of years, the time referred to was fixed in advance.
In Gen. 50:3, “And they fulfilled forty days for him...” Again a definite time is meant.
In Lev. 8:33, the days of ordination that are fulfilled are fixed at 7.
To summarize the remaining evidence for a definite term of days: Lev. 12:4, Lev. 25:29; Num. 6:5, 6:13; Tobit 8:20; Tobit 10:1; 1Mac. 3:49;
Evidence for a number of days less than exact or not exactly predetermined: 2Sam. 7:12 (speaking of death). 1Chron. 17:11 (speaking of death). Lam. 4:18 (speaking of death). In all these cases the text speaks of the day of a person’s death.
Now we should distinguish the words used in Greek to mean “fulfill.” There are two words πίμπλημι and πληρόω. The first word means “to cause to be completely full” (BDAG, 3rd edition), and the second simply means “to fill up.” The former word is used in Luke 1:23, 2:6, 2:21, 2:22. In every case an exact number of days is meant. But it appears to be more intensive than πληρόω. It means full in a sense of satiate, glut, satisfy, have enough. See LSJ. BDAG, 3rd edition, suggests it has to do with gestation periods, and cites Herodotus who gives the time at ten months. This has to be 9 lunar months and 1 day at a minimum, which is 266 days. The ancients counted inclusively, so the 10th month was the month for giving birth. By choosing πίμπλημι in four cases with “days” Luke appears to have placed more emphasis on the matter of a fixed term. And we see that in 3 of the cases, the number of days is stated in Scripture, 7 for a division service, 8 for circumcision, and 33 for purification. So the highest probability is that Luke had the fixed number of days for gestation in mind, which is 266 days, or 9 lunar months and 1 day. We see that this probability is widely confirmed by the use of the idiom with days and fill in other places, with no unqualified exceptions in Luke, and the only other seeming exception having to do with the day of a person’s death.
So now we can show how to use this probability. Since Tishri 1, 2 BC was the birth date of Messiah (cf. Rev. 12:1-2), then a full term back of this date is Dec. 10, 3 BC, or the first day of month 10 (X.1). This leaves exactly five months for Elıshaνa. So X.1 = month 6 for Elıshaνa. This fit is constrained by the division of Aνıyah ending July 13, 3 BC, and shows that Yoɦanan was conceived July 14th, or the first day of month V.