Biblical Calendar Year Length 364 vs 365 Days

The length of the biblical calendar year is a complex topic, with various traditions and interpretations regarding whether it consisted of 364 or 365 days. The Bible itself does not explicitly state a fixed number of days for a year, but it does indicate that the sun and moon were appointed to mark out years ^[4].

Ancient Hebrews used two main ways of reckoning the year: a sacred calendar, beginning around the vernal equinox with the month Abib, and a civil calendar, starting around the autumnal equinox with the month Tishri ^[2]. From the time of the Exodus, a year was instituted where Abib became the first month ^[1]. While the essential characteristics of this year can be determined, the exact length of any single year is not fixed in the biblical text ^[1]. Early computations of time by years are noted in Genesis, such as the length of patriarchal lives ^{[3, 4]}.

Some traditions suggest a year of 360 days was in use during Noah's time ^[1]. However, later Jewish traditions, particularly rabbinic and philosophical, discuss both lunar and solar years. A lunar year, consisting of twelve lunar months, totals approximately 354 days, 8 hours, 48 minutes, and 36 seconds ^{[5, 14, 15]}. In contrast, a solar year is understood to consist of 365 days ^{[5, 6, 14, 15]}. The Babylonian Talmud, for instance, discusses a nazirite vow taken for a solar year as 365 days and for a lunar year as 354 days ^{[14, 15]}.

The need to reconcile the lunar year with the solar year led to the practice of intercalation, adding an extra month to the lunar year to align it with the solar cycle ^[5]. Maimonides, in his Mishneh Torah, describes a nineteen-year cycle for the fixed calendar, which includes seven leap years and twelve ordinary years. This structure is designed so that the total number of days, including hours and units, equals nineteen solar years, each of 365 days and six hours (or 365 and 1/4 days) ^{[9, 12]}. He also notes an opinion among the Sages that a solar year is slightly less than 365 and one-quarter days, specifically 365 days, 5 hours, 997 units, and 48 moments ^[10].

The Talmud also records a teaching from Rabbi Abba in the name of Shmuel, stating that one does not count days to make up years, but rather counts months to make up years, based on Exodus 12:2 ^{[7, 8, 11]}. This highlights the emphasis on lunar months as the primary units for reckoning the year in certain Jewish legal contexts. The concept of a 365-day solar year is also mentioned in prophetic contexts, such as Rabbi Yehuda HaNasi's statement that the messianic era will last 365 years, corresponding to the number of days in a solar year ^[13].

Sources

Smith's Bible Dictionary “Smith's Bible Dictionary: Year — the highest ordinary division of time. Two years were known to, and apparently used by, the Hebrews. + A year of 360 days appears to have been in use in Noah's time. + The year used by the Hebrews from the time of the exodus may: be said to have been then instituted, since a current month, Abib, on the 14th day of which the first Passover was kept, was then made the first month of the year. The essential characteristics of this year can be clearly determined, though we cannot fix those of any single year. It was essentially solar for the offering of productions”
Easton's Bible Dictionary “Easton's Bible Dictionary: Year — Heb. shanah, meaning "repetition" or "revolution" (Gen. 1:14; 5:3). Among the ancient Egyptians the year consisted of twelve months of thirty days each, with five days added to make it a complete revolution of the earth round the sun. The Jews reckoned the year in two ways, (1) according to a sacred calendar, in which the year began about the time of the vernal equinox, with the month Abib; and (2) according to a civil calendar, in which the year began about the time of the autumnal equinox, with the month Nisan. The month Tisri is now the beginning of the Jew”
Genesis “The days of Isaac were one hundred eighty years. -- Genesis 35:28”
Torrey's Topical Textbook “Torrey's Topical Textbook: Years — The sun and moon appointed to mark out -- Ge 1:14. Early computation of time by -- Ge 5:3. Divided into Seasons. -- Ge 8:22. Months. -- Ge 7:11; 1Ch 27:1. Weeks. -- Da 9:27; Lu 18:12. Days. -- Ge 25:7; Es 9:27. Length of, during the patriarchal age -- Ge 7:11; 8:13; 7:24; 8:3. Commencement of, changed after the exodus -- Ex 12:2. Remarkable Sabbatical. -- Le 25:4. Jubilee. -- Le 25:11. In prophetic computation, days reckoned as -- Da 12:11,12. Illustrative (Coming to,) of manhood. -- Heb 11:24. (Well stricken in,) of old age. -- Lu 1:7. (Being full of,) of ol”
Sefaria (Jewish (Kabbalistic/Philosophical)) “Ramban (Nachmanides) on Exodus 13:2: SANCTIFY UNTO ME. This means that they are to consecrate the firstborn at once so that the commandment be applicable in the wilderness. This chapter adds many commandments: that they remember the day [when they left Egypt] and that the month was Aviv, 364 Verses 3-4. and that they keep this ordinance in its season . 365 Verse 10. This is an allusion to the intercalation [of an extra month] in the lunar year, 366 A lunar year — i.e., twelve lunar months — totals 354 days, 8 hours, 48 minutes and 36 seconds, as opposed to the solar year, which consists of 365”
Sefaria (Jewish (Kabbalistic/Philosophical)) “Ramban (Nachmanides) on Genesis 1:14: AND YEARS. The luminaries are to complete their orbit and then traverse again the same course they followed, thus making the solar year consist of 365 days and the lunar year consist of [lunar cycles, each approximately] 30 days.”
Babylonian Talmud (Jewish (Rabbinic)) “Babylonian Talmud, Megillah 64b.9:10: Having mentioned a teaching of Rabbi Abba in the name of Shmuel, the Gemara cites another of his statements: And Rabbi Abba said that Shmuel said: From where is it derived that one does not count days to make up years, i.e., a year is considered to be comprised of either twelve or thirteen lunar months, and not 365 days? As it is stated: “Of the months of the year” (Exodus 12:2), which indicates that you count months to make up years, but you do not count days to make up years.”
Babylonian Talmud (Jewish (Rabbinic)) “Babylonian Talmud, Megillah 64a.9:10: Having mentioned a teaching of Rabbi Abba in the name of Shmuel, the Gemara cites another of his statements: And Rabbi Abba said that Shmuel said: From where is it derived that one does not count days to make up years, i.e., a year is considered to be comprised of either twelve or thirteen lunar months, and not 365 days? As it is stated: “Of the months of the year” (Exodus 12:2), which indicates that you count months to make up years, but you do not count days to make up years.”
Mishneh Torah (Maimonides) (Jewish (Rabbinic)) “Mishneh Torah (Maimonides), Mishneh Torah%2C Sanctification of the New Month 6:10: [The fixed calendar is structured in] a nineteen-year cycle, including seven leap years and twelve ordinary years. This is called a machzor . Why was this [structure] chosen? Because when you total the number of days in twelve ordinary years and seven leap years together with their hours and their units, counting all [sums of] 1080 units as an hour, [all sums of] twenty-four hours as a day, and adding them to the number of days, the total will equal nineteen solar years, each of these years being 365 days and si”
Mishneh Torah (Maimonides) (Jewish (Rabbinic)) “Mishneh Torah (Maimonides), Mishneh Torah%2C Sanctification of the New Month 10:1: According to the opinion among the Sages of Israel that a solar year is less than [365 and] one-quarter [days], there is a view that [the length of the solar year] is 365 days, 5 hours, 997 units, and 48 moments. A moment is a seventy-sixth portion of a unit. According to this reckoning, the difference between a solar year and a lunar year will be 10 days, 21 hours, 121 units, and 48 moments (in numbers, 10 - 21 - 121 - 48). [According to this calculation,] there will be no remainder at all after a [nineteen-yea”
Babylonian Talmud (Jewish (Rabbinic)) “Babylonian Talmud, Megillah 5a.10: Having mentioned a teaching of Rabbi Abba in the name of Shmuel, the Gemara cites another of his statements: And Rabbi Abba said that Shmuel said: From where is it derived that one does not count days to make up years, i.e., a year is considered to be comprised of either twelve or thirteen lunar months, and not 365 days? As it is stated: “Of the months of the year” (Exodus 12:2), which indicates that you count months to make up years, but you do not count days to make up years.”
Mishneh Torah (Maimonides) (Jewish (Rabbinic)) “Mishneh Torah (Maimonides), Mishneh Torah%2C Sanctification of the New Month 9:2: According to the opinion that [a solar year] is [exactly] 365 and 1/4 days, there will be a remainder of one hour and 485 units after every nineteen-year cycle, as we mentioned. 4 Chapter 6, Halachah 10. Between the start of each of the successive seasons of the year, there will be ninety-one days and seven and one-half hours. When you know the date and the hour of the beginning of one season, you can calculate [the beginning of] the following season by [adding the above amount]. Similarly, you can calculate the ”
Babylonian Talmud (Jewish (Rabbinic)) “Babylonian Talmud, Sanhedrin 99a.7: Rabbi Yehuda HaNasi says: The messianic era will last 365 years, corresponding to the number of days of the solar year, as it is stated: “For the day of vengeance is in My heart, and the year of My redeemed is come” (Isaiah 63:4).”
Babylonian Talmud (Jewish (Rabbinic)) “Babylonian Talmud, Arakhin 68a.18:14: The Gemara raises an objection against Shmuel from a baraita . If one says: I am hereby a nazirite for a duration that is like the number of days in a solar year, he counts 365 days for his term of naziriteship, corresponding to the number of days in a solar year. If he says: Like the days in a lunar year, i.e., a year comprising twelve lunar months, he counts 354 days for his term of naziriteship, corresponding to the number of days in a lunar year. The Gemara explains the objection: And if it is so, that there can be eight full months in a year, there ar”
Babylonian Talmud (Jewish (Rabbinic)) “Babylonian Talmud, Arakhin 68b.18:14: The Gemara raises an objection against Shmuel from a baraita . If one says: I am hereby a nazirite for a duration that is like the number of days in a solar year, he counts 365 days for his term of naziriteship, corresponding to the number of days in a solar year. If he says: Like the days in a lunar year, i.e., a year comprising twelve lunar months, he counts 354 days for his term of naziriteship, corresponding to the number of days in a lunar year. The Gemara explains the objection: And if it is so, that there can be eight full months in a year, there ar”

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