Adjusting Times for Time Zones

David collects data from two locations, one on the East coast and the other on the West coast. After collecting the East coast times, he needs to adjust them for the time zone differences. He is wondering how to adjust the East coast times by three hours, so they represent West coast times.

How to adjust an East coast time by three hours to be consistent with West coast times depends on the nature of the times you are adjusting. In general, if the data is stored as an Excel date/time serial number, then the adjustment is easy. All you have to do is remember that in the serial number format, anything to the left of the decimal point is days and anything to the right of the decimal point is partial days (hours, minutes, and seconds).

Since an hour is 1/24 of each day, three hours would be 3/24, or 0.125. Simply subtract this value from the serial value stored in the worksheet, and you've adjusted the time for the difference in time zones. The actual formula is easy:

=A1-0.125

You have to be a bit careful in doing this sort of adjustment with your date/time serial numbers, however. If the values in the worksheet are simply time values (there is no date component to the left of the decimal point), then subtracting 0.125 from the time value can result in an erroneous result if the original time is anywhere between midnight and 3:00 am. The way around that is to make the formula just a bit more complex:

=IF(A1<0.125,A1+0.875,A1-0.125)

If the value in A1 is strictly a time value, between midnight and 3:00 am, the formula adds 21 hours (21/24 or 0.875) to the value, providing the expected result of an adjusted time between 9:00 pm and midnight.

ExcelTips is your source for cost-effective Microsoft Excel training. This tip (9309) applies to Microsoft Excel 2007, 2010, 2013, 2016, 2019, and 2021. You can find a version of this tip for the older menu interface of Excel here: Adjusting Times for Time Zones.