#Roman dates were counted inclusively forward to the next one of three principal days within each month:

#Kalends: the 1st day of each month

#Nones: the 7th day of "full months" and 5th day of hollow ones, 8 days—"nine" by Roman reckoning—before the Ides in every month.

#Ides: the 15th day of "full months" and the 13th day of hollow ones, one day earlier than the middle of each month.

https://en.wikipedia.org/wiki/Roman_calendar