Why are some years 12 months and others 13?

Leap years (7 in every 19, following the Metonic cycle) add a 13th month, Adar II. In non-leap years, "Adar" alone is month 12.

How accurate is the arithmetic calendar?

For the printed Jewish calendar this is the authoritative algorithm — printed luachs match it exactly. It is the same code used by major calendar software.

Why does the tool not handle sunset?

Sunset varies by latitude and date, so any rule would be wrong somewhere. Add a day to your Gregorian input if you need the Hebrew date starting at sunset.

Anno Mundi ("in the year of the world") — the standard Hebrew calendar era, counting from the traditional date of creation.

Hebrew Calendar Converter

Convert between Gregorian and Hebrew dates with arithmetic Hebrew calendar rules.

Written by Golam Rabbani, Founder & Lead Engineer

This interactive tool requires JavaScript. Read the formula and worked example below; you can compute the result by hand.

How to use this hebrew calendar converter

Pick the direction: Gregorian → Hebrew, or Hebrew → Gregorian.
Enter the Gregorian date, or enter the Hebrew year, month, and day.
Press "Convert".
Read the formatted result with the Hebrew month name and numeric breakdown.
Use Copy to share or Reset to start over.

About this hebrew calendar converter

The Hebrew calendar is a lunisolar calendar: months follow the moon, but a 13th month (Adar II) is inserted in 7 of every 19 years to keep the year aligned with the seasons. This tool implements the standard arithmetic Hebrew calendar described by Reingold and Dershowitz in <em>Calendrical Calculations</em>, which uses only integer arithmetic — no astronomical observations are required. The same formulae are used by most Jewish calendar software and by the Hebrew calendar in Unicode CLDR.

Conversion goes both ways. A Gregorian date is first mapped to a Rata Die fixed-day number, then walked into the Hebrew year, month, and day using the molad (new-moon) calculation, the four "dechiyot" postponement rules, and per-year month-length variations (Cheshvan and Kislev can each be 29 or 30 days depending on the year). The reverse direction reuses the same primitives. Months are reported with their canonical names — Nisan, Iyar, Sivan, Tammuz, Av, Elul, Tishrei, Cheshvan, Kislev, Tevet, Shevat, Adar (or Adar I and Adar II in leap years).

Worked example: convert 2026-05-28 (Gregorian) to Hebrew. The tool reports 11 Sivan 5786 AM. Convert 1 Tishrei 5787 AM (Rosh Hashanah next year) back and it gives 12 September 2026.

The Hebrew day starts at sunset, so the tool reports the Hebrew date that <em>contains</em> the given Gregorian midnight; if you need the post-sunset date, advance the Gregorian date by one before converting.

FAQ

Why are some years 12 months and others 13?: Leap years (7 in every 19, following the Metonic cycle) add a 13th month, Adar II. In non-leap years, "Adar" alone is month 12.
How accurate is the arithmetic calendar?: For the printed Jewish calendar this is the authoritative algorithm — printed luachs match it exactly. It is the same code used by major calendar software.
Why does the tool not handle sunset?: Sunset varies by latitude and date, so any rule would be wrong somewhere. Add a day to your Gregorian input if you need the Hebrew date starting at sunset.
What does AM mean?: Anno Mundi ("in the year of the world") — the standard Hebrew calendar era, counting from the traditional date of creation.