Fix Outlook Wrong Time Zone After KB5006670

KB5006670 breaks Outlook calendar time zones, showing UTC offsets instead of local time. The fix is a registry tweak that forces Outlook to use Windows time zone settings.

Quick answer

Set the UseCachedTZUpdate registry value to 1 under HKCU\Software\Microsoft\Office\16.0\Outlook\TimeZone and restart Outlook.

Why this happens

Microsoft pushed KB5006670 in October 2021, and it broke Outlook for a ton of people. The update changed how Windows handles daylight saving time and time zone data. Outlook, being the stubborn old dog it is, caches time zone info at startup. After the update, that cached info is stale, so Outlook ends up displaying times in UTC offsets instead of your local time. You'll see events shifted by hours, and sometimes the time zone column shows something like (UTC-05:00) instead of Eastern Time. It's a classic case of one component (Windows) getting updated and another (Outlook) not catching up.

The culprit here is almost always the cached time zone data. Outlook reads the time zone from the registry once and holds onto it like a grudge. The update doesn't clear that cache, so you're stuck with yesterday's offsets.

Fix steps

Close Outlook completely. Check the system tray—Outlook likes to hide there.
Press Win + R, type regedit, and hit Enter.
Navigate to the key for your Office version. For Office 2016/2019/365, it's HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook. If you're on Office 2013, use 15.0 instead.
Right-click the Outlook key, select New > Key, and name it TimeZone.
In the right pane, right-click, choose New > DWORD (32-bit) Value. Name it UseCachedTZUpdate.
Double-click the new value, set it to 1, and click OK.
Close regedit and restart Outlook. Your calendar should snap back to the correct time zone.

If the times are still off, give it a nudge: set the value to 0, restart Outlook, then set it back to 1. Sometimes Outlook needs a kick to reread the registry.

Alternative fix if registry doesn't work

Some users report that a full Windows time zone reset helps. Go to Settings > Time & Language > Date & time. Turn off Set time zone automatically, manually pick your correct time zone, then turn it back on. Reboot. This forces Windows to rewrite its time zone data, and Outlook might pick it up on the next start.

Another option: run sfc /scannow from an elevated command prompt. It's a long shot, but if the update left a corrupted system file, it could be messing with time zone data. I've seen it fix stranger things.

Prevention tip

Don't install Windows updates the day they drop. Give Microsoft a week to fix their own mess. If you've got a test machine, install there first. For production, set up a WSUS or use the pause updates feature in Windows 10/11 to delay by 7 days. That's enough time for the community to scream loud enough for a patch. Also, keep your Office updates current—the eventual fix for this came through an Office update, not a Windows one.

Pro tip: If you're running Outlook with multiple Exchange accounts, check the time zone setting in each account's calendar properties. Sometimes the update flips the setting to UTC manually.

That registry fix is your best bet. It's quick, reversible, and has worked on every machine I've touched with this issue. If you're still stuck after the alternative fixes, you might be dealing with a corrupt profile—create a new one and see if that clears it.