Amidora · Library
How can Adar I and Adar II be distinguished in a Hebrew leap year?
5784 is a leap year because (7 × 5784 + 1) mod 19 is 0; keep Adar I and Adar II apart, as the converter does with its adar-i and adar-ii identifiers.
How the converter names the months
The converter has 14 month identifiers: the twelve regular months plus adar-i and adar-ii. A common year uses adar; a leap year uses adar-i and adar-ii instead, and the converter refuses any identifier the chosen year does not have. The result also carries a leap-year flag, calculated as (7 × year + 1) mod 19 below 7.
For 5784 the remainder is 0, so it is a leap year. For 5785 it is 7, so that year is common, and for 5787 it is 2, so the next leap year after 5784 is 5787.
Year lengths follow the same pattern: counting from one 1 Tishrei to the next, 5784 has 383 days and 5785 has 355.
Worked example
The civil date 24 February 2024 converts to 15 Adar I 5784 in this date-only calculation.
- Hebrew year
- 5784
- Hebrew month
- Adar I
- Day
- 15
- Leap year
- Yes
Worked example
The civil date 24 March 2024 converts to 14 Adar II 5784. The two examples should not both be saved under an undifferentiated “Adar” label.
- Hebrew year
- 5784
- Hebrew month
- Adar II
- Day
- 14
Saving a leap-year date
- Convert the civil date and read the month identifier, not just the month name.
- Save the year, the identifier and the day together.
- When reading an old record that says only Adar, check the year's leap flag before converting it.
- Keep any event time and place separately when its day boundary matters.
Adar across three years
The two examples above fall in 5784. In the following year, 2025-03-14 converts to 14 Adar 5785, with no numeral, because 5785 has a single Adar. Two years later, 2027-03-01 converts to 22 Adar I 5787. Entering adar for 5784, or adar-ii for 5785, is refused.
- 2025-03-14
- 14 Adar 5785
- 2027-03-01
- 22 Adar I 5787
- 5784 · adar
- refused
- 5785 · adar-ii
- refused
Mistakes
- Saving Adar for a 5784 date and losing which Adar was meant.
- Picking a month by its position in a twelve-item list.
- Assuming leap years come every other year; 5785 and 5786 are both common.
- Treating the leap flag as information about observance dates.
Boundary
These are civil-date conversions without a sunset boundary. The ECMA-402 DateTimeFormat and Hebcal documents listed below describe the calendar; which date to use for an anniversary is a separate question for the appropriate calendar and guidance.