1,274. Calculating Subsequent Years

Hilchos Kiddush HaChodesh 6:8

If the molad for a given year is known and one adds the appropriate remainder – either that of a regular year or that a leap year as called for – it will yield the time of the molad for the following year. This process may likewise be followed from year to year forever. We start with the molad of the year of creation, which was Monday night, five hours and 204 chalakim after nightfall, abbreviated as “2, 5, 204.” This is the point from which all these calculations proceed.

Hilchos Kiddush HaChodesh 6:9

The following rules apply to all the calculations for the times of the molad. When the remainders are added, when the sum of 1,080 chalakim is reached, it is counted as one hour and added to the number of hours. When the sum of 24 hours is reached, it is counted as a day and added to the number of days. When the number of days exceeds seven, it is subtracted from the sum and only the remainder is used in the calculations. This is because we have no need to know the number of days, just on which day of the week the molad will occur, at which hour and how many chalakim.