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.
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.
| 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.
| 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. |
| 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.
| 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.
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 20 August 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.
| 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 3 m 17 d | Common year — 12 months | Bar Mitzvah: |
| Born 24 February 2013 — born in Adar of a common year | 14 Adar 5773 | 13 y 5 m 23 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 5 m 23 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 8 m 7 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.