start_date: starting date serial value
end_date: ending date serial value
method: counting method
DAYS360 returns the number of days from start_date to end_date.
If method is 0, the default, the MS Excel (tm) US method will be used. This is a somewhat complicated industry standard method where the last day of February is considered to be the 30th day of the month, but only for start_date. If method is 1, the European method will be used. In this case, if the day of the month is 31 it will be considered as 30 If method is 2, a saner version of the US method is used in which both dates get the same February treatment.
This function is Excel compatible.