The first step in computing a sentence is to calculate the number of days from the start of the sentence until the end of the sentence. All dates are calculated using the calendar. The number of days in a month or the number of days in a year is determined by the calender; so that a year in 1999 is 365 days and a year in 2000 is 366 days. A month in January is 31 days, while a month in June is 30 days When the number of days in a sentence is calculated, it is necessary to include the starting day as one day of time served. So that a two day sentence starting January 1st would end January 2nd. It is incorrect to add 2 days to January 1st to equal January 3rd.