Comparing dates ?

What approach is easy and simple.
Comparing date with another date ?
OR
Comparing date with a number ?
For example: Let's say I need to do compare a date field with 3 months of expiration date
DO ( something )
WHERE dateField is < date2field (date2field will hold another date)

OR

DO ( something )
WHERE dateField is < fieldNUMBER (fieldNUMBER will hold a number 3 which will represents no. of months but I guess in this situation how we will mention in code that 3 is number of months ?)

Please advice ?

...