Please Note: This article is written for users of the following Microsoft Excel versions: 97, 2000, 2002, and 2003. If you are using a later version (Excel 2007 or later), this tip may not work for you. For a version of this tip written specifically for later versions of Excel, click here: Automatically Converting to GMT.

Automatically Converting to GMT

Written by Allen Wyatt (last updated June 15, 2022)
This tip applies to Excel 97, 2000, 2002, and 2003


4

GMT is an acronym for Greenwich Meridian Time, which is a reference time for the world; it is the time in Greenwich, England, and is sometimes referred to as "Zulu time." (Zulu is the phonetic name for zero, and the zero refers to the longitude of Greenwich, England.)

You may have a need to convert a local time to GMT in your worksheet. If you always know that the time will be entered in local time, this can be done quite easily with a formula. For instance, assume that you are entering the local time in cell B7, and that you are in the Pacific time zone. In this time zone, you are either seven or eight hours behind GMT, depending on if daylight savings time is in effect. The following formula will adjust the time entered in B7 by either seven or eight hours, depending on whether the date associated with the time is within the period of daylight savings time.

=IF(AND(B7>=DATEVALUE("3/8/2009 02:00"),B19<=
DATEVALUE("11/01/2009 02:00")),B7+7/24,B7+8/24)

Remember that whenever you enter a time into a cell, Excel automatically attaches a date to it. Thus, if you enter a time of 10:15 into a cell, and the day you make the entry is January 17, then Excel automatically converts the entry in the cell to 01/17/2009 10:15:00. This is done even though you may only be displaying the time in the cell—in Excel, every date has a time associated with it, and every time has a date associated with it.

Because of this entry behavior, Excel would use the formula just shown to do the proper adjustment based on the default date when you enter a time (today's date) or a date you may explicitly enter.

The only drawback to this formulaic approach is that you must remember to change the daylight savings time boundary dates from year to year. (The ones in the formula are for 2009.) You could change the formula so that you actually stored the boundary dates in cells, such as E1 and E2, as follows:

=IF(AND(B7>=$E$1,B19<=$E$2),B7+7/24,B7+8/24)

While the formula is shorter, it still has a problem with the rather static determination of when daylight savings time begins and ends—you must remember to update that information manually. In addition, if you move to a different time zone, you must remember to modify the values by which the date and time are adjusted.

A really handy way around these drawbacks is to create a user-defined function that accesses the Windows interface and determines what the system settings are in your computer. Your system keeps track of daylight savings time automatically, as well as which time zone you are in. Accessing this information through a user-defined function means you will never need to worry about those items in your worksheet. You can use the following macro to do just that:

Option Explicit

Public Declare Function SystemTimeToFileTime Lib _
  "kernel32" (lpSystemTime As SYSTEMTIME, _
  lpFileTime As FILETIME) As Long

Public Declare Function LocalFileTimeToFileTime Lib _
  "kernel32" (lpLocalFileTime As FILETIME, _
  lpFileTime As FILETIME) As Long

Public Declare Function FileTimeToSystemTime Lib _
  "kernel32" (lpFileTime As FILETIME, lpSystemTime _
  As SYSTEMTIME) As Long

Public Type FILETIME
    dwLowDateTime As Long
    dwHighDateTime As Long
End Type

Public Type SYSTEMTIME
    wYear As Integer
    wMonth As Integer
    wDayOfWeek As Integer
    wDay As Integer
    wHour As Integer
    wMinute As Integer
    wSecond As Integer
    wMilliseconds As Integer
End Type

Public Function LocalTimeToUTC(dteTime As Date) As Date
    Dim dteLocalFileTime As FILETIME
    Dim dteFileTime As FILETIME
    Dim dteLocalSystemTime As SYSTEMTIME
    Dim dteSystemTime As SYSTEMTIME

    dteLocalSystemTime.wYear = CInt(Year(dteTime))
    dteLocalSystemTime.wMonth = CInt(Month(dteTime))
    dteLocalSystemTime.wDay = CInt(Day(dteTime))
    dteLocalSystemTime.wHour = CInt(Hour(dteTime))
    dteLocalSystemTime.wMinute = CInt(Minute(dteTime))
    dteLocalSystemTime.wSecond = CInt(Second(dteTime))

    Call SystemTimeToFileTime(dteLocalSystemTime, _
      dteLocalFileTime)
    Call LocalFileTimeToFileTime(dteLocalFileTime, _
      dteFileTime)
    Call FileTimeToSystemTime(dteFileTime, dteSystemTime)

    LocalTimeToUTC = CDate(dteSystemTime.wMonth & "/" & _
      dteSystemTime.wDay & "/" & _
      dteSystemTime.wYear & " " & _
      dteSystemTime.wHour & ":" & _
      dteSystemTime.wMinute & ":" & _
      dteSystemTime.wSecond)
End Function

This may look imposing, as is often the case when working with system calls, but it works wonderfully. There are three system routines referenced (SystemTimeToFileTime, LocalFileTimeToFileTime, and FileTimeToSystemTime). By setting up the calls and using them in order, the date and time are automatically adjusted to GMT. To use the function, in your worksheet you would enter this to convert the time in cell B7:

=localtimetoutc(B7)

Format the cell as date/time, and the output is exactly what you wanted.

ExcelTips is your source for cost-effective Microsoft Excel training. This tip (2185) applies to Microsoft Excel 97, 2000, 2002, and 2003. You can find a version of this tip for the ribbon interface of Excel (Excel 2007 and later) here: Automatically Converting to GMT.

Author Bio

Allen Wyatt

With more than 50 non-fiction books and numerous magazine articles to his credit, Allen Wyatt is an internationally recognized author. He is president of Sharon Parq Associates, a computer and publishing services company. ...

MORE FROM ALLEN

Two-Line Headings in a TOC

If you use the TC field to mark what goes in a TOC, you may wonder why if you mark two lines together with the field they ...

Discover More

Formatting Axis Patterns

Create a chart in Excel and you can then modify it almost any way you desire. One modification is to adjust the color or ...

Discover More

Making Custom Heading Styles Appear in the Navigation Pane

Creating styles for your documents is a powerful way to format them. How do you get paragraphs formatting with those ...

Discover More

Professional Development Guidance! Four world-class developers offer start-to-finish guidance for building powerful, robust, and secure applications with Excel. The authors show how to consistently make the right design decisions and make the most of Excel's powerful features. Check out Professional Excel Development today!

More ExcelTips (menu)

Breaking Up Variable-Length Part Numbers

Part numbers can often be long, made up of other component elements. Breaking up part numbers into individual components ...

Discover More

Converting UNIX Date/Time Stamps

If you import information generated on a UNIX system, you may need to figure out how to change the date/time stamps to ...

Discover More

Shortening ZIP Codes

US ZIP Codes can be of two varieties: five-digits or nine-digits. Here's how to convert longer ZIP Codes to the shorter ...

Discover More
Subscribe

FREE SERVICE: Get tips like this every week in ExcelTips, a free productivity newsletter. Enter your address and click "Subscribe."

View most recent newsletter.

Comments

If you would like to add an image to your comment (not an avatar, but an image to help in making the point of your comment), include the characters [{fig}] (all 7 characters, in the sequence shown) in your comment text. You’ll be prompted to upload your image when you submit the comment. Maximum image size is 6Mpixels. Images larger than 600px wide or 1000px tall will be reduced. Up to three images may be included in a comment. All images are subject to review. Commenting privileges may be curtailed if inappropriate images are posted.

What is 7 + 0?

2021-09-07 23:39:46

Peter

Why not get the time from an internet server?
This is covered by https://myengineeringworld.net/2013/09/retrieve-time-from-internet-server-vba.html. The code discussed there would need some minor adaptation since it generates local time from server time.


2021-09-04 11:23:30

Tomek

The current version of Excel (MS365) does not attach the current date when you enter time. As a result the date of such entry becomes a funny date: 1900-01-00.


2019-04-06 16:51:46

Eyal Peleg

Hi,
This line of code:
LocalTimeToUTC = CDate(dteSystemTime.wMonth & "/" & _
dteSystemTime.wDay & "/" & _
dteSystemTime.wYear & " " & _
dteSystemTime.wHour & ":" & _
dteSystemTime.wMinute & ":" & _
dteSystemTime.wSecond)

makes some assumptions on the local format of date & time.
specifically in some regiones (including my own) it is custom to use day/month/year and not month/day/year,
this becomes a problem, ecpecially on dates when the day is smaller then 13 - causing a return of the wrong date.

I suggest changing this to

LocalTimeToUTC = CDate(DateSerial(dteSystemTime.wYear, dteSystemTime.wMonth, dteSystemTime.wDay) + _
TimeSerial(dteSystemTime.wHour, dteSystemTime.wMinute, dteSystemTime.wSecond))

which does not have those problems.

also note that if you are running on a 64bit version of office you need to add PtrSafe (case sensitive !) ineach Declare

i.e. 3 times Public Declare PtrSafe Function ...

otherwise thanks for a very helpful piece of code


2018-03-03 10:40:21

Randy Austin

Thanks very much for this. Quite helpful.


This Site

Got a version of Excel that uses the menu interface (Excel 97, Excel 2000, Excel 2002, or Excel 2003)? This site is for you! If you use a later version of Excel, visit our ExcelTips site focusing on the ribbon interface.

Newest Tips
Subscribe

FREE SERVICE: Get tips like this every week in ExcelTips, a free productivity newsletter. Enter your address and click "Subscribe."

(Your e-mail address is not shared with anyone, ever.)

View the most recent newsletter.