How can I restrict the date range to 3 months?

With the code below, I can restrict the date range on a day-by-day basis, but this filtering is invalid for some months because it is on a day-by-day basis.



I have examined the date methods as below, but I could not find a method to limit it to 3 months.

nextMth(today);

prevMth(today);

...

How can I make a month-based 3 month restriction with date functions?