Converting a time in Microsoft Excel 2013 to or from Greenwich Mean Time requires a basic understanding of what GMT is and how it differs from the time zone you are converting it to. With this knowledge, you can convert any time to GMT or convert GMT to another time zone by adding or subtracting the time difference.
GMT is a time zone used by the U.K. and some African countries, representing the mean solar time at the Royal Observatory in Greenwich, London. It was the world's first time standard until 1960, when it was replaced by Coordinated Universal Time, abbreviated UTC, as the world time standard. While GMT is now a time zone, just like Eastern or Mountain time, many people still refer to it as the standard, perhaps because it's synchronized with UTC.
The U.K. is not always on GMT. From March to October, the U.K. is on daylight saving time, known as British Summer Time, which is one hour later than GMT.
Converting Current Time to GMT
Enter Excel's NOW function by clicking a cell and typing =NOW(). By itself, the NOW function returns the current date and time based on your computer's clock. Unlike most other functions, nothing goes in the parenthesis.
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Calculate the number of hours between your current time zone and GMT. If you're located west of the U.K., add the time difference. If you're east of the U.K., subtract the hours. Because the NOW function is based on days, not hours, you need to add or subtract these hours from the NOW function divisible by 24 and then press Enter. For U.S. time zones, use:
- =NOW()+5/24 for the Eastern time zone.
- =NOW()+6/24 for the Central time zone.
- =NOW()+7/24 for the Mountain time zone.
- =NOW()+8/24 for the Pacific time zone.
If your time zone is currently using daylight saving time, add an additional hour.
Converting From GMT to Another Time Zone
To convert GMT to any other time zone, add or subtract the difference in hours divided by 24. Select the cell where you want the new time to appear, type =, followed by the cell containing the GMT and then add or subtract the time difference divided by 24. Press Enter. For U.S. time zones, use:
- =NOW()-5/24 for the Eastern time zone.
- =NOW()-6/24 for the Central time zone.
- =NOW()-7/24 for the Mountain time zone.
- =NOW()-8/24 for the Pacific time zone.
If the time zone that you want displayed is using daylight saving time, subtract an additional hour.