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Excel/converting # of days to actual date


I have calculated the actual number of days a certain process will take for example 150 days.  Now I want to calculate exactly what day (calendar days) that will be.  I run this report at the first of the month so I have a fixed start date.  

I want to know if on 5/1/14 the process takes 150 days what day will that be?

Thanks !


Excel Dates are stored as the number of days from a base date.  For windows, that is Midnight on 31 Dec 1899 as becomes 1 January 1900.  That really isn't of any significance.  What is of significance is that to add 150 days to a date, you do just that.  Add the number 150.

So if you have

5/1/14 in cell A1, then in cell B1 you can have  =A1+150 and format B1 as a date.

That produces 9/28/2014 in cell B1.  

Here is just a little more discussion/background information.  

If you format cell A1 as General, you see the number 41760.  This is the date serial number and represents the number of days since the base date.  Now I add 150 to it and get

41760 + 150 = 41910.

in any cell enter 41910 and format that cell as a date.  It should show Sept 28, 2014 in your chosen date format.  

You also should know that a date serial can have a decimal part like 41760.25  

this is 41760 and 1/4 days.  So 1/4 of a day is 6 hours and this represents 6 AM on 5/1/2014.  Just to show you how time is represented as well in conjunction with a date.

Tom Ogilvy  
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Tom Ogilvy


Selected as an Excel MVP by Microsoft since 1999. Answering Excel questions in Allexperts since its inception in 2001. Able to answer questions on almost all aspects of Excel's internal capabilities. If seeking a VBA solution, please specify that in your question itself so I give you the answer you want. [Excel has weak protection - if you are distributing an application, I don't answer questions on how to protect your project from your users.]


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