Talladega said:

Let me see, i just counted with my fingers.

1/6/2006 thru 12/2006 is 12 months

No, it isn't. Consider this: how many months are there from 1/6/2006 to

2/6/2006? The correct answer is: one. So it is 11 months from 1/6/2006 to

12/6/2006.

1/2007 thru 12/2007 is 12 months

Well, you skipped a month, namely: 12/6/2006 to 1/6/2007. So the next

period is 12/6/2006 to 12/6/2007, which is indeed 12 months.

1/2008 thru 12/2008 is 12 months

1/2009 thru 6/30/09 is 6 months

Again, you are skipping months. Those time periods should be 12/6/2007 to

12/6/2008 (12 months) and 12/6/2008 to 6/30/2009 (6 months and 24 days).

So the total is 11+12+12+6 = 41 months and 24 days.

all the months add up to 42.

That depends on how you want to treat additional time (24 days) beyond an

integral number of months. That's really up to you. There is no right or

wrong way; it all depends on your application (purpose). But you do need to

know what the tools (functions) do, and you need to make adjustments if

their "judgment" differs from you. Most functions are not mindreaders ;-).

DATEDIF truncates. If you want to round up, you might use some heuristic

like the following. Suppose 1/6/2006 is in A1 and 6/30/2006 is in B1.

Then:

=datedif(A1,B1) + (edate(A1,datedif(A1,B1))<>B1)

If you get a #NAME? error, see the Help page for the EDATE() function.

HTH.

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