Last reviewed on October 24, 2014   —  9 Comments

This is not really a bug but a limitation of the dual time zone display when daylight time goes into effect, and to a lesser degree, when we revert to standard time. Apparently, it's not a very common problem since very few people complain about it, but it's interesting.

Dual time zones and DSTWhen you use dual time zones in Outlook and the default zone is west of the secondary zone, an extra hour is added to the time scale offset for the Sunday DST goes into effect. If you view multiple dates and begin with that Sunday, the (incorrect) offset is used on the time scale so it appears Outlook has the times wrong.

For example, if your default time zone is Pacific and Eastern is your secondary time, when Sunday rolls around, the time scale incorrectly displays a 4 hr time difference all day. If you use a multi-day view with Sunday as the first day, the Sunday time scale is used, so it appears there is a 4 hour time difference each day.

This view anomaly occurs because the default is a zone west of the secondary and Outlook takes into consideration that DST goes into effect in the earlier time zone and adjusts the times using the wrong offset. The entire 24 hour period uses the same offset and the first day in the view determines the offset. This issue also affects the view when the time 'falls back' to standard time, but only if the dual time zones are 3 or more hours apart.

Fortunately Outlook uses GMT and time zone offsets to calculate appointment times and reminders are based off the default time zone, not the secondary zone, so it's unlikely to cause missed appointments (if you use reminders). When you open the appointments they appear at the correct time.

"Time heals all wounds" and it will fix this display problem – until then, use the work week view if you use the dual time zone feature and the default zone is west of the secondary zone.

DST Starts or Ends on different dates

When the two time zones start and/or end Daylight Saving time on different dates, the time scale will vary during the delta period. For example, Helsinki starts DST at the end of March while the US makes the change 2 weeks earlier, so during this 2 week period, the usual difference will be off by an hour, depending on which zone is set as primary. In the fall, there is a 1 week lag where the times will be off by an hour.

Outlook 2010 Dual time Swap bug

When you use Outlook 2010’s dual time zone feature and one time zone uses DST and the other does not, when you swap zones the Use DST checkbox in Window’s Date and Time applet may be unchecked when the time zone that uses DST is active. Because Outlook 2010 doesn’t display the Use DST checkbox, you won’t know this unless you happen to notice the computer’s time is off an hour.

Solution: Install Outlook 2010 SP1.

Video Tutorial

More Information

Outlook, Appointments and Time Zones

Meeting requests and appointments are off by one hour

Daylight Saving Time Updates

If you are having other appointment problems relating to time zones, see for more information.


  1. Philippe Jeanjean says

    Thank you, Diane!
    Yes, I am seeing that issue.
    I travel a lot between Paris and Boston and I just missed a phone call because of the bug :-(

    I just reported the bug thtough a Microsoft support feedback link.
    But I have a feeling it won't go anywhere.

    Anyway, thinks for confirming my suspicion.


    • Diane Poremsky says

      It's not going to go anywhere - it would be difficult to fix and the return is low: few people are affected (only people using dual zones), only for a short period. Reminders should be on the correct time.

      If a lot of people were affected, Microsoft would do more about - maybe popup a warning when DST kicks into effect or during the delta period when the EU and US is out of sync and dual zones are used. This bug has been in Outlook since day 1, but I only "discovered" it in 2008 when someone mentioned it in a forum. I see maybe 1 complaint each march.

  2. Mike says

    I ran into this also and it was driving me crazy until I saw this article. So thanks for that. In my case the left scale does not use DST at all, but it's really the same issue.

    But after reading this, I realize it's not a bug. I think "anomaly" is the better term. Here's the thing. If you display starting Sunday, the very beginning of Sunday is actually NOT DST. Remember, you set your clocks ahead at 2:00 am. So Sunday at midnight, technically, you are still on Standard time.

    The issue is, since you are displaying a grid that displays the week, and the time changes somewhere during that week (albeit very early in the week), then which scale do you display at the left side? One very logical answer is, "well, the scale in effect at the beginning of the week". Which is standard time. In fact, there is really no correct way to display this scale 100% correctly, because during the week, the time zones slide with respect to one another, so at least some portion of the week will be wrong.

    That's why when you select Work Week, and show starting on Monday, it all works properly. Monday at midnight, we are on DST. The entire displayed week has the same relative time difference, and all is well.

    Thanks again for sharing this was truly driving me nuts.

    • Diane Poremsky says

      Right, it's not really a bug. Not everyone agrees with me, but trying to account for the hour loss (or the hour gain in the fall) would be a major undertaking.

  3. DD says

    This article is another great example of why it is better to Google issues first, rather than rely on MS "help" searches. I wasted 45 mins on the MS site before my second Google search led me to this very helpful article. My issue is exactly what is described here - I didn't really isolate the issue until I noticed that the Outlook calendar view "Work Week" correctly showed a 3 hr difference between EDT and PDT, while the "Week" view (which starts on Sunday as described above) shows 4 hours. I guess I will use the Work Week view until next Sunday, when the anomoly will disappear. Thank you very much for posting!

  4. cdube85 says

    Fascinating. This was driving me nuts today. If you change the start of the week day to Monday, it reverts back to the correct display. I wish I'd learned that before screwing up a couple of meeting invitations.

  5. Guy says

    Just wasted the better part of an hour trying to figure this out after a meeting problem yesterday. The reverse is true in the Fall -- ET is only two hours ahead of PT.

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