Hebrew age: the Metonic cycle and the two months of Adar

The Hebrew calendar is lunisolar: its months follow the moon, and a thirteenth month is inserted seven times in every nineteen years so that the year as a whole keeps pace with the sun. That makes a Hebrew age straightforward to count and a Hebrew birthday occasionally difficult to place, because one month in the year does not exist every year.

If you do not know the time, noon changes only the hours. The place sets the time zone your birth instant is read in, which is what the figures below are computed from.

Observances

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Your Hebrew age and coming of age

Computed as of 29 September 2026. Where this calendar cannot answer for a date, it says so and gives the reason rather than extrapolating.

Worked example for a birth on 1 January 2000 (London): Hebrew — Twelve months in most years, thirteen in seven years out of nineteen.
Hebrew date of birth 23 Tevet 5760 A Hebrew day begins at sunset; this is the civil day.
Hebrew age 26 years, 8 months, 24 days
Year of birth A leap year, with two months of Adar
Bar Mitzvah 5 January 2013 — at 13 Hebrew years The Hebrew birthday, not thirteen solar years on.

See the same birth date in all nine calendars — Gregorian to the second, the other East Asian counts, Hijri, Hebrew, Solar Hijri and the planets.

Twelve months, or thirteen

Twelve lunar months fall about eleven days short of a solar year — the same gap that makes the Hijri calendar drift through the seasons. The Hebrew calendar closes it instead of letting it accumulate: seven years in every nineteen are leap years with a thirteenth month, which brings the two almost exactly back into line. Nineteen solar years and 235 lunar months differ by about two hours.

Which seven is fixed by arithmetic, not by observation. A Hebrew year is a leap year when (7y + 1) mod 19 is less than 7 — that is, at positions 3, 6, 8, 11, 14, 17 and 19 of the cycle.

One complete nineteen-year cycle, Hebrew years 5776 to 5794. The first day of each year is 1 Tishri, given here as a civil date; the day itself begins at sunset the evening before.
Hebrew year Position in the cycle Shape 1 Tishri
Hebrew year 5776 19 of 19 leap year, 13 months
Hebrew year 5777 1 of 19 common year, 12 months
Hebrew year 5778 2 of 19 common year, 12 months
Hebrew year 5779 3 of 19 leap year, 13 months
Hebrew year 5780 4 of 19 common year, 12 months
Hebrew year 5781 5 of 19 common year, 12 months
Hebrew year 5782 6 of 19 leap year, 13 months
Hebrew year 5783 7 of 19 common year, 12 months
Hebrew year 5784 8 of 19 leap year, 13 months
Hebrew year 5785 9 of 19 common year, 12 months
Hebrew year 5786 10 of 19 common year, 12 months
Hebrew year 5787 11 of 19 leap year, 13 months
Hebrew year 5788 12 of 19 common year, 12 months
Hebrew year 5789 13 of 19 common year, 12 months
Hebrew year 5790 14 of 19 leap year, 13 months
Hebrew year 5791 15 of 19 common year, 12 months
Hebrew year 5792 16 of 19 common year, 12 months
Hebrew year 5793 17 of 19 leap year, 13 months
Hebrew year 5794 18 of 19 common year, 12 months

The leap month is not added at the end of the year. It is inserted just before Adar, the last month of winter, and the two are then called Adar I and Adar II.

The two months of Adar

This is where a Hebrew birthday needs a rule rather than a lookup. Someone born in Adar of a common year has a birth month that, in a leap year, has become two months. Someone born in Adar I has a birth month that most years do not have at all.

The convention this site applies is the one that governs Purim, which falls on 14 Adar and is observed in Adar II when there are two. A birthday from a common-year Adar is therefore observed in Adar II, and a birthday from Adar I returns to the single Adar of a common year. This is the Ashkenazi ruling. Other authorities hold that a common-year Adar birthday belongs in Adar I, and the practice a family follows is a question for a rabbi rather than for a calculator — so every row below says which month it used.

A birthday on 14 Adar 5783, a common year — born 7 March 2023 — observed over the following seven Hebrew years.
Hebrew year Month observed in Civil date Why
Hebrew year 5784 14 Adar II A leap year has two months of Adar. This site observes a birthday from a common-year Adar in Adar II, following the Ashkenazi ruling; other authorities hold Adar I.
Hebrew year 5785 14 Adar A common year, with one Adar — the birth month exactly.
Hebrew year 5786 14 Adar A common year, with one Adar — the birth month exactly.
Hebrew year 5787 14 Adar II A leap year has two months of Adar. This site observes a birthday from a common-year Adar in Adar II, following the Ashkenazi ruling; other authorities hold Adar I.
Hebrew year 5788 14 Adar A common year, with one Adar — the birth month exactly.
Hebrew year 5789 14 Adar A common year, with one Adar — the birth month exactly.
Hebrew year 5790 14 Adar II A leap year has two months of Adar. This site observes a birthday from a common-year Adar in Adar II, following the Ashkenazi ruling; other authorities hold Adar I.
A birthday on 14 Adar I 5784, a leap year — born 23 February 2024 — observed over the following six Hebrew years. Adar I exists in only two of them.
Hebrew year Month observed in Civil date Why
Hebrew year 5785 14 Adar Adar I exists only in a leap year; in a common year the birthday falls in Adar.
Hebrew year 5786 14 Adar Adar I exists only in a leap year; in a common year the birthday falls in Adar.
Hebrew year 5787 14 Adar I A leap year, which has an Adar I — the birth month exactly.
Hebrew year 5788 14 Adar Adar I exists only in a leap year; in a common year the birthday falls in Adar.
Hebrew year 5789 14 Adar Adar I exists only in a leap year; in a common year the birthday falls in Adar.
Hebrew year 5790 14 Adar I A leap year, which has an Adar I — the birth month exactly.

Months that change length

Two months, Heshvan and Kislev, are 29 days in some years and 30 in others. The calendar uses them to absorb the adjustments that keep Rosh Hashanah off certain weekdays, which means a birth on 30 Kislev has a birthday that some years simply do not contain.

A birthday on 30 Kislev, observed over seven Hebrew years, with the length Kislev takes in each.
Hebrew year Length of Kislev Birthday observed on Civil date
Hebrew year 5784 29 days 29 Kislev (the last day of the month)
Hebrew year 5785 30 days 30 Kislev
Hebrew year 5786 30 days 30 Kislev
Hebrew year 5787 30 days 30 Kislev
Hebrew year 5788 30 days 30 Kislev
Hebrew year 5789 30 days 30 Kislev
Hebrew year 5790 29 days 29 Kislev (the last day of the month)

Where these dates come from

The Hebrew calendar as implemented in ICU/CLDR and reached through Intl.DateTimeFormat.

The Hebrew calendar has been arithmetic (not observational) since roughly the 4th century CE, so conversions are exact rather than approximate. Dates are civil days: a Hebrew date properly begins at sunset the evening before, which this site does not model.

To check the method: ICU User Guide — Calendar Services; Unicode CLDR Project.

The sunset point matters more here than the phrasing suggests. A Hebrew date runs from sunset to sunset, so someone born on a Tuesday evening has a Hebrew birth date that this site will show as Tuesday's and that most observance would place on Wednesday's. Getting that right needs the sunset time at the place of birth, which this site does not compute; if the birth was after dark, take the Hebrew date here as the day before the one you want.

Which month an Adar birthday belongs to is a matter of practice rather than of arithmetic, and is described above rather than settled here. Prose last reviewed 2026-08-20.

Worked examples

Ages as they stand on 29 September 2026 in Jerusalem, computed when this page was built. The coming-of-age date is a Hebrew anniversary — 13 Hebrew years for a Bar Mitzvah, 12 for a Bat Mitzvah — and not thirteen solar years after the birth, which would miss by a week or more.

Hebrew ages on 29 September 2026, Asia/Jerusalem, for four birthdates.
Birthdate Hebrew birth date Hebrew age Year shape at birth Coming of age
Born 15 May 1990 — an ordinary date in both calendars 20 Iyar 5750 36 y 4 m 27 d Common year — 12 months Bar Mitzvah:
Born 24 February 2013 — born in Adar of a common year 14 Adar 5773 13 y 7 m 4 d Common year — 12 months Bat Mitzvah:
Born 23 February 2024 — born in Adar I, which most years do not have 14 Adar I 5784 2 y 7 m 4 d Leap year — 13 months Bar Mitzvah: — Adar I exists only in a leap year; in a common year the birthday falls in Adar.
Born 31 December 2024 — born on 30 Kislev, a day that only some years have 30 Kislev 5785 1 y 9 m 18 d Common year — 12 months Bar Mitzvah:

Counting from creation

Hebrew years are counted anno mundi, from a traditional date of creation, which is why the numbers are in the 5700s while the Gregorian year is in the 2000s. A Hebrew year begins at Rosh Hashanah in the northern autumn, so it straddles two Gregorian years and the difference between the two era numbers is 3760 or 3761 depending on the time of year.