Example:
If Booking date is -> 7 June 2017, I want the formula to calculate the current month (June) + 3 months(90 days), and the formula should return 29th September 2017
Calculating as follows:
June + 90 days [31 days in July + 31 days in August + 28 days in September].
This formula is to be used in a process builder to set a expiry date.