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Excel/Calculating the average date from a list of dates with different years


QUESTION: Hello Mr, Umlas,

I have a list of 310 study stations and the dates that they were sampled over the past six sampling years (one sample date per station per year).  I am trying to calculate the average month/day that each station was sampled over the past six sampling years.  For example, station 1 was sampled on 8/12/1995, 8/15/1998, 7/25/2001, 8/13/2004, 8/11/2007, and 7/30/2010 and I need to calculate the average month/day (as well at the variation) the station has been sampled over the past sampling years.  I cannot find a solution online and my attempts have been unsuccessful.  

I am happy to provide you with any additional information that you need.  Any advice that you can offer would be greatly appreciated.  

Thank you for your time.


ANSWER: Just take the average:
I get 2/6/2003.

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QUESTION: Thank you for your reply but that's not exactly what I am looking for.  I just want the average month/day...the year is not relevant.  

I used the formula =IF(ISNUMBER(B2), MONTH(B2)&"/"&DAY(B2), "") to extract just the month and day but if I try to average, I get #DIV/0!.  This happens even if I copy and paste only the values.  

Thank you again for your time,


MONTH(B2)&"/"&DAY(B2) will give you a TEXT string, like 8/12, not really a number, so when you average all the text strings you do get #DIV/0!
Try this (works:)
and fill down, and take the average.
The 2000 is totally an arbitrary year, but allows you to get the real average. You can format these all as M/D, and you'd see:
with an average of
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Bob Umlas


I`m a Microsoft Excel MVP (Most Valuable Professional) and have been since the inception of the program in 1995. I can answer every kind of Excel question except: API, Importing/exporting to other programs (powerpoint, word,...) Also check out my in-person training link at


Worked with MS Excel since version 0.99 (on the Mac!). Was contributing editor to Excellence Magazine, having written >300 articles. John Walkenbach said of me "I finally met someone who knows as much about Excel as I do."

Excellence, The Expert, Microsoft

BA in math, Hofstra University, 1965

Awards and Honors
Led sessions for the Convergence 2004-2006 seminar on Excel tips & tricks

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