Difference between Two dates (months)

[anshul_900]

I need to calculate the difference between two dates in months. I am using the intck function to calculate it with the 4th arguement (method = 'C') but I think the 4th argument just works in case of years. I want to calculate precisely how much is the difference in number of months. For Instance No of Months between 1st July 2018 and 31st dec 2018. The intnx function is returning 5 but which is not correct since its actually over 5 months ( 1 day short of 6 months to be precise). Is there a way to do that? 

[VDD]

add +1.

when you have end_date - start_date you need to account for the starting boundary.

[PaigeMiller]

Yes, you could calculate the number of months and the number of days in that last fractional month, you would get something like 5 months and 30 days. Is that what you want?

I think the 4th argument just works in case of years

Incorrect.

[Reeza]

---

@anshul_900 wrote:

I need to calculate the difference between two dates in months. I am using the intck function to calculate it with the 4th arguement (method = 'C') but I think the 4th argument just works in case of years. I want to calculate precisely how much is the difference in number of months. For Instance No of Months between 1st July 2018 and 31st dec 2018. The intnx function is returning 5 but which is not correct since its actually over 5 months ( 1 day short of 6 months to be precise). Is there a way to do that? 

---

It depends, but you need to be careful of the definition. There is no standard definition of 'month', some have 28 and some have 31 days. That difference can be a big difference when doing comparisons, so this means your data isn't really comparable. For doing survival analysis at a research centre we had settled on using 365.25/12 as the # of days in a month. All that really matters is that you're clear with the definiton you want to use. 1 month and 2 days could be February plus 2 days in January or March, or it could be December which has 31 days and both would be equal. 

[ballardw]

---

@anshul_900 wrote:

I need to calculate the difference between two dates in months. I am using the intck function to calculate it with the 4th arguement (method = 'C') but I think the 4th argument just works in case of years. I want to calculate precisely how much is the difference in number of months. For Instance No of Months between 1st July 2018 and 31st dec 2018. The intnx function is returning 5 but which is not correct since its actually over 5 months ( 1 day short of 6 months to be precise). Is there a way to do that? 

---

The 'C' does not work only with annual. but since your stated example is comparing the first of one month with end of another it may be hard to see what the difference is between 'C' and 'D'. Maybe an examination of this output will shed some light:

data example;
   do sdate= '01Jul2018'd to '31Dec2018'd;
      monthsc = intck('month',sdate,'10Dec2018'd,'C');
      monthsd = intck('month',sdate,'10Dec2018'd,'D');
      output;
   end;
   format sdate date9.;
run;

Pay attention to the differences as SDATE moves from the 9 to 10 and 11 of each month.

And what about when you compare 30NOV2018 to 1Dec2018 and get 1 "month" difference? Do you want to round that down because it is only one day?

And you may be learning why some financial processes use a "year" of 360 days with 30 day "months".

[Astounding]

If you really want fractional months, why go through INTCK?  Why not just convert number of days:

n_mon = (end_dt - start_dt) / 30.5;

There are more precise formulas, but this one should be close enough.