Formula to calculate days, dates

To Whom It May Concern

I want to create a formula that will return a date - eg 25 December 2014 - by simply typing in the current (today's) date.

Let me give you an example of how I intend to use it.

I am a certified Civil Marriage Celebrant (CMC), couple's who present before me requesting to be married, must present documentation (known as the) "Notice of Intended Marriage (NOIM)" to me according to the following criteria:

The NOIM must be given to the authorised celebrant (me) no earlier than 18 months and no later than one month before the (intended) date of the marriage.

Take the date of this message: 12 October 2014 (for future reference, this will be known as the "current date").

So, where the formula is concerned, I want to be able to enter the current date and return the result (calculation) equaling the (see) example above.

I trust this is easy to understand; if not, I'll try and simplify it, in response to any replies.

Thank you.

Matthew Hinds (Australia)