# of Months between two dates

[ankit.singh at 42hertz.com]

On Sunday, August 8, 2010 at 11:46:51 PM UTC+5:30, MRAB wrote:
> Greg Lindstrom wrote:
> > I work for a company that processes claims for the health care industry 
> > (Novasys Health, recently purchased by Centene Corp).  My current 
> > assignment has me writing a routine to compute insurance premiums.  One 
> > of the requirements is to determine how many months a policy has been in 
> > effect.  The datetime module will give me the number of days but, with 
> > months having different lengths, that does not do me much good.  I've 
> > looked in the calendar library but didn't see anything there, either.
> > 
> > I've written a function to return the months between date1 and date2 but 
> > I'd like to know if anyone is aware of anything in the standard library 
> > to do the same?  For bonus points, does anyone know if postgres can do 
> > the same (we use a lot of date/time funcitons in postgres, already, but 
> > didn't see this problem addressed).
> > 
> [snip]
> A simple expression is:
> 
>      diff = (current_year - start_year) * 12 + (current_month - start_month)
> 
> According to this, if a policy started on 31 July 2010, then on 1 August
> 2010 it has been in effect for 1 month. Is this reasonable? It depends!
> 
> It's probably better to write the function yourself according to what
> makes sense in your use-case, and document its behaviour clearly.

Thanks for that answer