Excel - how to show a negative time calculation

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I am creating a time sheet that calculates the time used against a starting amount of hours purchased for consulting. I have used the "time" calculation to delete the time used. I have now got to where negative time has been used from the hours purchased. The help section tells me to switch to the "1904 data system" to allow the formula to show a negative number. I have gone to Excel File but do not see the "option" that is explained in help.


Any other suggestions.


For Example: The client has purchased 20 hours of consulting time. 

2 Replies


In the desktop version of Excel for Windows:

Select File > Options.

Select Advanced in the navigation pane on the left.

Scroll down to the section 'When calculating this workbook'.



In Excel for Mac, the 1904 date system is the default setting.


Another option is to use formula as here


and apply number format to the resulting cell.