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Many Excel questions are about dates and times. Here are a very few common questions:

  1. Excel Time Calculations
    1. How do I add times together?
    2. How do I subtract time?
    3. How do I sum the time data in the format: 5:20, 12:02, 20:12 etc. to get 50:07?
    4. I'm adding cells with seconds, i.e. 25, 50, etc... the result I'd like is 1:10
    5. I need to calculate 0:45 minutes at 120 per hour - with an answer of 90.
    6. How do I calculate the hours worked for a shift that ends after midnight?
  2. Excel Date Calculations
    1. How can I enter the date into a cell so it doesn't change every day?
    2. When I copy and paste Excel dates, they end up one day/four years wrong.
    3. How do I add 3 months to an Excel date?
    4. What worksheet functions would emulate EOMONTH; last day of month?
    5. Excel thinks 1900 is a leap year. It's not
  3. Excel Date and Time Resources
    1. Where can I find more information on Excel dates and times?

1. Excel Time Calculations

How do I add times together?

Just add together like any number (=A1+A2+A3). Use custom number format [h]:mm in the result cell to prevent rollover at 24 hours (see the screen shot in question "When I try to sum the time data..." below.)

How do I subtract time?

Just subtract, like =B1-A1. Use Calendar format 1904 if you need to display negative results; Tools/Options/Calculation and check the 1904 Date System checkbox. Note that 1904 calendar will offset all dates by 4 years 1 day, so be careful.

When I try to sum the time data in the format: 5:20, 12:02, 20:12 etc. I get the value that is the real sum minus N*24, e.g.. 2:07 instead of 50:07.

Use the custom number format [h]:mm to prevent rollover at 24 hours

I'm adding up a large number of cells with seconds in them, i.e... 25, 50 47, etc... the result I would like is 1:10, 1:50: 2:03

Since XL stores times as fractions of days, in order to convert integers into times you need to divide the sum by (24*60*60) or 86,400

I need to calculate a column with hh:mm (formatted for TIME) against a hour rate. So 0:45 minutes needs to be calculated against 120 per hour - with an answer of 90. Now it says 3.75?

1 is a day; 24 hours. So one hour is 1/24. =A1*B1*24 will bring the desired result. Format result cell as currency or number (it tends to pick the date format by default).

How do I calculate the hours worked for a shift that ends after midnight?

If the start time is greater than the end time, we'll assume that the shift ended the next day. In that case, we'll add 1 to the end time, which is the equivalent of adding a full day to the end time. That makes the end time greater than the start time, and the calculation will work correctly.
For example, with start time in cell B2 and end time in cell C2, use this formula:

=IF(C2="",0,IF(B2>C2,1,0)+C2-B2)

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2. Excel Date Calculations

How can I enter the date into a cell so it doesn't change every day?

To enter the current date, press Ctrl + ;   (hold the Ctrl key while typing a semicolon.)
To enter the current time, press Ctrl + :   (hold the Ctrl key while typing a colon.)

When I copy and paste Excel dates, they end up one day wrong.
When I copy and paste dates, they end up four years wrong.

One workbook is using 1904 calendar, the other one 1900 (in the first example, years are not displayed, but definitely present). Go menu Tools>Options, Calculation and make them equal, preferably also correct if you know what the dates was supposed to be.

How do I add 3 months to an Excel date?

=DATE(YEAR(A1),MONTH(A1)+3,DAY(A1))

Could someone give me the series of worksheet functions that would emulate EOMONTH; last day of month?

The last day of the month equals the zero'th of next month for some strange reason: =DATE(YEAR(A1),MONTH(A1)+1,0)

Excel thinks 1900 is a leap year. It's not.

Yes it does and it's not. The following MSKB article explains the reason:
     Excel 2000 incorrectly assumes that the year 1900 is a leap year
        http://support.microsoft.com/kb/214326

3. Excel Date and Time Resources

Where can I find more information on Excel dates and times?

Chip Pearson's web page on dates and times will give you an understanding of how this works in Excel , and it has lots of useful date and time samples.

 

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Original FAQs compiled by Harald Staff, Excel MVP 2000-2005. Additions by Debra Dalgleish.

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Debra Dalgleish

Last updated: September 12, 2013 12:09 AM