Set hardware clock to UTC on Windows (or how to make the clock work on a Mac Book Pro)

I recently bought a Mac Book Pro since I can now dual boot OS X and Windows XP. The only real issue that I've had is that OS X, like most Unices likes to set the hardware clock to UTC time. This causes the clock in Windows XP to be off by 5 hours (I'm in the central US timezone).

I recently discovered a registry tweak that will tell Windows to interpret the hardware clock as UTC time:

Windows Registry Editor Version 5.00


Just save the above reg script into a .reg file and import it to set your clock to UTC time. You can still set your timezone for the clock and have the correct time displayed. This can also be usefull if you are dual booting XP with any other Unix variations that like to set the harware clock to UTC. I usually run Linux and such in VirtualPC/VMWare so I havnt actually tried it with Linux.


It would seem that there are still some issues with this:

It seems to work most of the "time" for me but 1 or twice a day the clock changes to the timezone offset again. I just have to do a w32tm /resync /nowait to fix it. My suspicion is that the clock applet in the tray is monkeying it up.


  • Hi,
    Thanks for your post. However, I can't seem to get the w32tm /resync /nowait thing to work. I execute that command in the command prompt, and it says "The command completed successfully," but the clock on the tray doesn't change. Any thoughts?

  • Actually it seems that the latest version of BootCamp has fixed this problem so I don't use the above method anymore. I'm also running Vista now instead of XP.

  • I now set windows to hide the clock in the tray until this is resolved. I only use windows for gaming and anytime it comes out of standby it changes the time... or whenever it feels like it.

  • Thanks, That worked great

  • Excellent! Thanks a ton. I used to set Linux to use local time, but when I added OS X to the party I knew I had to figure out how to change OS X or change Windows. Since I wanted UTC, I changed Windows by using your registry entry.

  • Thanks, fixed me a few problems

  • Seems Microsoft can't do simple math,
    I currently have NTP sync on and UTC hardware clock enabled.
    but my clock is ALWAYS 5mins fast, ntp sync fixes it for a while until something happens and changes back.

    for the last 3 days in a row, the clock has been consistently out by 5mins, NTP manual sync fixes it, until I notice the next day that it has gone forward 5mins, and it'll stay at on 5mins fast for months.

  • I set that on XP some time ago but after we went on DST the TZ went back to non-DST every day although I corrected it by hand and set up a NTP server.

  • I have beeing scouring that the google for this info and simply needed to thank

    you for that the post. BTW, simply off topic, how can I find out a

    duplicate of this theme – Thanks

  • Doesn't seem to work anymore. The registry editor on Win7 complains that the file needs to be in binary mode.

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