Calends

The calends (Latin: kalendae, "the called") were the first days of each month of the Roman calendar. The Romans assigned these calends to the first day of the month, signifying the start of the new moon cycle. On that day, the pontiffs would announce at the Curia Calabra the number of days until the upcoming month at which time the debtors had to pay off their debts that were inscribed in the kalendaria, a sort of accounts book. The date (in this calendar system) was measured forward to upcoming days such as the calends, nones or ides. Thus, while modern calendars count the number of days after the first of each month, III. Kal. Ian. would be December 30th, three days (counting inclusively) before the first of January. To find the day of the calends of the current month, one counts how many days remain in the month, and add two to that number. For example, April 22, is the 10th of the calends of May, because there are 8 days left in April, to which 2 being added, the sum is 10.

Computation of the days of the month from calends can be done using the following verses: