Very, very mundane. Quite pointless, yet a factual question.
When saying something like, “one month later,” how is it reckoned? Is it 31 days later, or is it on the same date of the next month (for instance February 4 - March 4)?
One of those perplexing questions…
Depends on usage, I do not believe there is one true answer. I base this from having read many discussions on the matter on the SAS-L list. SAS is a big data analysis program, and does a lot of date caluclations. How you use it depends on your situation.
Example:
Jan 31, 2001 + 1 month could be figured as:
Adding 31 days to get March 3rd, 2001.
Adding “1 month” to get Feb 31, 2001, resulting in an error.
Adding “1 month” to get Feb 31, which rolls over to March 1st.
Adding “1 month” to get Feb 31, which rolls back to Feb 28th.
And do you check for leap year or not?
All of these are valid depending on the context of your situation.
1 month also could be considered a standard 30 days (why 31?), could be however many days are in the current month, however many days in the next month, 365/12, 365.25/12, days in current year divided by 12 — again all might be valid.
Since the days in a month are variable (from 28 to 31) it can’t have an exact meaning. When I set up a payment in my personal accounting program and set it for “monthly” it applies the payment on the same day each month… not every 30 or 31 days apart.