Why does Tishrei have month number 7 instead of 1?

The Hebrew year for counting purposes begins in Tishrei (around September), but the months are traditionally numbered from Nisan in spring, which the Torah calls the first month. So Nisan is month 1 and Tishrei is month 7, even though the year number increments at Tishrei.

How does the converter handle leap years?

Hebrew leap years, which occur 7 times in a 19-year cycle, add a thirteenth month. In those years the month otherwise called Adar splits into Adar I (month 12) and Adar II (month 13). The tool detects leap years automatically and labels the months accordingly.

What are the postponement rules?

The date of Rosh Hashana can be pushed back by one or two days to prevent certain holidays falling on awkward weekdays. The converter applies all the standard dechiyot rules through the molad calculation, so Rosh Hashana always lands on the canonically correct day.

Why do Hebrew years have different lengths?

A common year can be 353, 354 or 355 days and a leap year 383, 384 or 385 days. The variation comes from whether Cheshvan and Kislev have 29 or 30 days, which is determined so the calendar stays aligned with both moon and sun and obeys the postponement rules.

Is the day counted from sunset?

In Jewish practice the day begins at sunset the previous evening. This converter maps whole civil dates to whole Hebrew dates, so for an event after nightfall you may want the next Hebrew date. The conversion itself is calendar-accurate for the daytime portion of the date.

Gregorian ↔ Hebrew Date Converter

The Hebrew calendar is lunisolar: months follow the moon while leap months keep the year aligned with the sun. This converter translates a date between the Gregorian and Hebrew systems using the same molad-based arithmetic and postponement rules that fix the calendar, so the results match printed Jewish calendars exactly.

How it works

Both dates are converted to a common day count (a fixed-day or Rata Die number), then back into the target calendar:

1. Find the molad-based count of months elapsed to the target year
2. Derive the day of 1 Tishrei, then apply the postponement rules
3. Add month lengths (Cheshvan/Kislev variable, Adar split in leap years)
4. The result is the fixed day; convert it to the other calendar

Leap years are identified by the rule that year y is a leap year when (7y + 1) mod 19 is less than 7 — that places 7 leap years in each 19-year cycle.

Example and tips

Converting 2025-09-23 returns 1 Tishrei 5786 — Rosh Hashana. Converting 1948-05-14 returns 5 Iyyar 5708, the Hebrew date of Israeli independence. In a leap year, entering month 12 yields Adar I and month 13 yields Adar II; in a common year, month 12 is simply Adar. Remember that the Hebrew day starts at sunset, so for evening events the corresponding Hebrew date is the following one.