Date custom formatting for 30 days in each month

[hidaren]

Hey guys,

My government considers 30 days for each months when it comes to payments (ignores the 31th days of some months) which proved problematic for me to make some calculations regarding the salary of the workers, I need to know if there's a way to create a custom calendar system or modify the existing ones to make a year in which all months are 30 days, or if there's a way to exclude certain days (31th day of each month) from =datedif function, or something like that.

 

[Legacy 143009]

I don't know your data structure but you can use something inside DATEIF function:

=DATEDIF(Start_Date,IF(DAY(End_Date)>30,DATE(YEAR(End_Date),MONTH(End_Date),30),End_Date),"Y")

 

[hidaren]

I don't know your data structure but you can use something inside DATEIF function:

=DATEDIF(Start_Date,IF(DAY(End_Date)>30,DATE(YEAR(End_Date),MONTH(End_Date),30),End_Date),"Y")

Well, every female employee who gives birth to a new baby, will be paid an extra monthly salary until her baby reaches 6 years old, yet, there are some conditions:
1. every month should be considered as precisely 30 days, even if the month is 31 days in reality, still 30 days should be counted.
2. the 3 months of summer must be excluded if the employee is a teacher since they don't go to work during this period.
and some other conditions which are not of concern here

I've already made a series of formulas using a series of cells that meets the needs of other conditions yet, still, there's a flaw in the procedure which can only be solved by a calendar in which months are exactly 30 days. I want to know if there's a way to make such a calendar or modify the existing ones in the "format cell" tab to make this possible?