topic Re: Calculate difference between dates in months with decimals in SAS Programming

Calculate difference between dates in months with decimals

hovliza — Thu, 14 Dec 2017 12:50:58 GMT

Hi! If I want to calculate the difference between months I use this syntax;

*months;
DATA want;
SET have;
months=intck("month", start, end);
RUN;

But you only get the months without decimals. Is there an easy way to get the months with for example 2 decimals?

Re: Calculate difference between dates in months with decimals

Kurt_Bremser — Thu, 14 Dec 2017 13:04:48 GMT

Fractions of what? 31-day months, 30-day months, 28- or 29-day months?

I'd rather use days. A day is a day is a day.

Re: Calculate difference between dates in months with decimals

PaigeMiller — Thu, 14 Dec 2017 13:06:01 GMT

I guess that depends on how you define the word "easy".

The problem is that decimal months are not really defined; in fact, because some months have 30 days and some months have 31 days and some months have 28 or 29 days, I don't think you will find a unique answer, and I don't think there is anything programmed into SAS that will provide decimal months.

Nevertheless, you can create your own definition of decimal months and write data step code to make this happen.

Re: Calculate difference between dates in months with decimals

hovliza — Thu, 14 Dec 2017 13:12:17 GMT

Okay, thanks for the suggestions. I'd hoped for a procedure or something. But for now I'm going to use this syntax;

DATA want;
SET have;
months=(end-start)/(365.25/12);
RUN;

Re: Calculate difference between dates in months with decimals

RW9 — Thu, 14 Dec 2017 14:33:13 GMT

That's both assuming an average for year and for month. How accurate do you need it to be? May not be a suitable calculation for some.

Re: Calculate difference between dates in months with decimals

ballardw — Thu, 14 Dec 2017 15:30:53 GMT

And ignores leap years.

Re: Calculate difference between dates in months with decimals

ballardw — Thu, 14 Dec 2017 15:40:47 GMT

@hovliza wrote:

Hi! If I want to calculate the difference between months I use this syntax;
*months;
DATA want;
SET have;
months=intck("month", start, end);
RUN;
But you only get the months without decimals. Is there an easy way to get the months with for example 2 decimals?

Please describe exactly how you plan on using that fractional month part of the value.

Anything I have worked on that needed a different interval worked much better by dropping to an actual different interval, either weeks, biweekly period, days or even 5-day periods. That way at least handles 0.1month = one of .28, .29, .30 or .31.

Note that the intck and intnx functions supports multiples of the interval such as DAY3 or WEEK2 so you can easily specify a consistent period.