Dual-Boot Clock Wrong Between Windows and Linux? Make Windows Use UTC
Every time you boot Windows after Linux (or vice-versa) the clock is off by a few hours, then “fixes itself” on the next sync.
Why: Linux treats the PC’s hardware (RTC) clock as UTC and applies your time-zone offset, while Windows treats it as local time. Each OS rewrites the hardware clock its own way, so they disagree. The cleanest fix is to make Windows also read the hardware clock as UTC.
Fix 1: Tell Windows to treat the hardware clock as UTC
- Press Win + R, type
regedit, press Enter (accept the admin prompt). - Go to:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\TimeZoneInformation- Right-click in the right pane > New > DWORD (32-bit) Value, name it exactly
RealTimeIsUniversal. - Double-click it, set Value data to
1, click OK. - Reboot. Windows now interprets the hardware clock as UTC, matching Linux, so the time stays correct across both.
After this, leave your time zone set normally in Settings > Time & language > Date & time.
Fix 2: Or make Linux use local time instead
If you’d rather not touch Windows, configure Linux to write local time to the hardware clock so it matches Windows’ default. On most modern distributions:
timedatectl set-local-rtc 1 --adjust-system-clockUse one approach or the other — not both — or they’ll fight again.
FAQ
Should I pick the Windows fix or the Linux fix? The Windows-UTC approach (Fix 1) is generally preferred, because UTC is the standard for the hardware clock and avoids daylight-saving glitches.
After enabling RealTimeIsUniversal I can’t change the system time manually. That’s expected behavior — with this entry enabled, manually setting the system time may revert to the CMOS/hardware clock. Adjust the time in your BIOS/UEFI if you need to change the hardware clock itself.
Do I still get internet time sync? Yes, Windows still syncs over the network; the registry value only changes how it interprets the hardware clock.