What does a Hebrew year look
like?
An ordinary (nonleap) year has
353, 354, or 355 days. A leap year has 383, 384, or 385 days. The
three lengths of the years are termed, "deficient'',
"regular'', and "complete'', respectively.
An ordinary year has 12 months, a
leap year has 13 months.
Every month starts
(approximately) on the day of a new moon.
The months and their lengths are:
Name 
Length in a
deficient year 
Length in a
regular year 
Length in a
complete year 
Tishri 
30 
30 
30 
Heshvan 
29 
29 
30 
Kislev 
29 
30 
30 
Tevet 
29 
29 
29 
Shevat 
30 
30 
30 
Adar I 
30 
30 
30) 
Adar II 
29 
29 
29 
Nisan 
30 
30 
30 
Iyar 
29 
29 
29 
Sivan 
30 
30 
30 
Tammuz 
29 
29 
29 
Av 
30 
30 
30 
Elul 
29 
29 
29 
Total: 
353 or
383 
354 or
384 
355 or
385 
The month Adar I is only
present in leap years. In nonleap years Adar II is simply
called ``Adar''.
Note that in a regular year the
numbers 30 and 29 alternate; a complete year is created by adding
a day to Heshvan, whereas a deficient year is created by removing
a day from Kislev.
The alteration of 30 and 29
ensures that when the year starts with a new moon, so does each
month.
What years are leap years?
A year is a leap year if the
number year mod 19 is one of the following: 0, 3, 6, 8,
11, 14, or 17.
The value for year in this
formula is the ``Anno Mundi'' described below.
