How to use it
- Choose Gregorian date to Hebrew or Hebrew date to Gregorian in Convert.
- Type the Gregorian date, or the Hebrew year, Hebrew month and Day of the month.
- Read the Converted date and the Weekday of the Gregorian date.
- Open Months of this Hebrew year to see the length of each month and the Gregorian day it starts on.
How the months are counted
Each month begins with the molad, the mean new moon. A mean month is 29 days, 12 hours and 793 parts long, with 1080 parts to the hour, so twelve months make about 354 days. The count starts with the molad of year 1, a Monday, 5 hours and 204 parts after the Hebrew day began at 6 pm on the Sunday before.
The molad of Tishrei in year Y comes floor((235 × Y − 234) ÷ 19) months after that first molad, using the 19-year cycle of 235 months.
molad of Tishrei (Y) = 5 h 204 parts into day 1 + floor((235 × Y − 234) ÷ 19) × (29 days 12 h 793 parts)Leap years and the postponements
A year is a leap year with thirteen months when the remainder of (7 × Y + 1) ÷ 19 is 6 or less. That makes years 3, 6, 8, 11, 14, 17 and 19 of each nineteen-year cycle leap years, and the extra month is Adar I, with Adar II after it.
The first day of the year, 1 Tishrei (Rosh Hashanah), falls on the day of the molad, but four rules move it. A molad at or after noon moves it one day on. It never falls on a Sunday, Wednesday or Friday. A common year whose molad is a Tuesday from 9 h 204 parts moves to Thursday, and a year after a leap year whose molad is a Monday from 15 h 589 parts moves to Tuesday.
Year lengths and the length of each month
A common year has 353, 354 or 355 days, and a leap year has 383, 384 or 385. Cheshvan and Kislev take 29 or 30 days so that the year reaches its length. The other months are fixed: Tishrei 30, Tevet 29, Shevat 30, Adar 29 (Adar I 30 in a leap year), Nisan 30, Iyar 29, Sivan 30, Tammuz 29, Av 30 and Elul 29.
What this calculator does not cover
- Times of day and the exact moment a festival starts. The page gives whole days, from the evening before.
- Local custom and the rules of other Jewish calendars, such as the Karaite and the Samaritan calendars.
- The sighting of the new moon in ancient Israel, which the fixed calculation replaced.
Worked example: 3 October 2024
Choose Gregorian date to Hebrew, keep the date 2024-10-03, and read the converted date. The Hebrew year is 5785, a common year, so Cheshvan and Kislev follow the length of the year.
The leap test is (7 × 5785 + 1) mod 19 = 7, which is not 6 or less, so the year is common with twelve months.
| Gregorian | Hebrew | Weekday |
|---|---|---|
| 3 October 2024 | 1 Tishrei 5785 | Thursday |
Frequently asked questions
What kind of calendar is the Hebrew calendar?
It is a lunisolar calendar: its months follow the moon, and a thirteenth month in seven years out of nineteen keeps the years in step with the seasons. Its years are counted from the creation, as the Anno Mundi era.
Why does a Hebrew day begin in the evening?
A Hebrew day begins at 6 pm the evening before, in the general reckoning used here. The molad times are counted from that start, so a date can change in the evening.
What is a leap year in the Hebrew calendar?
A leap year has thirteen months and an extra Adar. The leap years of each nineteen-year cycle are years 3, 6, 8, 11, 14, 17 and 19 of that cycle.
Why do Cheshvan and Kislev change length?
The length of the year is 353, 354 or 355 days in a common year, and the rules move a day between Cheshvan and Kislev to reach that length, so the two months have 29 or 30 days.
Does a calculated Hebrew date match the date my community keeps?
Usually, but not always. Festival days can depend on local custom and on the observance of each community, so check the day with your community or synagogue.
Is the date I type sent to a server?
No. The calculation runs in your browser. Nothing you type is stored or sent to us, and you can use the page without an account.
Sources
Figures and text last checked on Tuesday, November 10, 2026.