# Mathematics of the Jewish Calendar/The calculation of the Molad

## The starting point

According to tradition, there was a Molad at exactly 14 hours (i.e. 8am) on the Friday of Creation, the time that Adam was created. Projecting the current rule back to that date, it follows, since Rosh Hashana cannot fall on a Friday (see later), that the following day was not only the first Shabbat but the first Rosh Hashana. This is regarded as Rosh Hashana of Year 2, since the six days of creation must belong to some year, which is designated as Year 1.

Working backwards, the previous Molad of Tishri was on a Monday, i.e. Day 2, at 5 hours and 204 chalakim. (With days from midnight to midnight, this is actually 11 hours 204 chalakim on Sunday pm.) Writing 2, 5, 200, 4 in Hebrew characters gives us BeHaRaD, so this is known as Molad BeHaRaD. It is also sometimes called Molad Tohu ("without form"), since it occurred while the world was still "without form and void" (Genesis ch.1). The date of this molad, and of Rosh Hashana for Year 1, would have been Monday 7 September 3761 BCE in the Gregorian calendar (7 October in the Julian one). (Note: when working with dates BCE, remember that there was no year 0; 1 BCE was immediately followed by 1 CE. Thus, the interval from say 1 June, 5 BCE to 1 June, 5 CE is only nine years, not ten.)

The date and time of each Molad, or time of New Moon, is computed by adding the standard interval 29 days, 12 hours, 793 chalakim to the date and time of the previous one.

If you are only interested in the day of the week and time of the molad, you can discard four weeks or 28 days and just add 1 day, 12 hours, 793 chalakim. If the result is 8 days or more, subtract a week.