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# Overdue invoice? 3 easy 'date math' tips

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in The Office Tech Pro

Most people, if asked whether a date in an Excel spreadsheet is text or a value, may tilt their heads and give an answer that sounds more like a question. Well, dates are actually numbers. The number associated with a date is the number of days it is past January 1, 1900. Take the date July 4, 2011. To Excel, even though you may see it as 7/4/2011, it is actually 40,728. If I ask, “Can I subtract 40,902 from 40,728?” you would tell me I could. But, if I asked, can I subtract 7/4/2011 from 12/31/2011, you might not be so sure. Well, the answer there is also , yes.

Between two dates
With 7/4/2011 in  cell A1 and 12/31/2011 in cell B1, I can type this formula in cell C1 to find out that there are 180 days between the 4th of July and New Year’s Eve.

Between date and today
If you always want to find out how many days past due an invoice might be, you could use this function TODAY() in cell E2 subtracting the Invoice Due.

Calculating a future or past date
If you know that a follow-up call will be made to a client in 45 days, you can add 45 to the Last Contact Date in D1 in a formula in E2.

Another great application for date math in Excel is project task tracking. Learn more about this and other project management capabilities of Excel kin our latest  webinar, Microsoft Excel for Project Management. Click here to register.

{ 3 comments… read them below or add one }

Trisha Lowman August 11, 2011 at 10:37 am

Thanks for the great tip!

-- The editors, Business Management Daily August 9, 2011 at 2:46 pm

Thanks, Karen for pointing that out…the formatting is now fixed!