Windows 10 Clock Resets After Reboot – The Real Fix

1. Dead CMOS Battery – The Most Common Culprit

If your clock resets every single time you restart, the CMOS battery is almost always the problem. This little coin-cell battery keeps the BIOS clock running when the PC is off. Once it dies, the clock forgets everything.

Here's how you can check: restart your PC, go into BIOS (usually F2 or Del key during boot), and look at the system date and time. If it's showing 1/1/2000 or something like that, the battery is dead. Replace it.

What you need: A CR2032 battery. Costs like $2. Open your PC case, find the battery on the motherboard, pop it out with a small flathead screwdriver, and put the new one in. That's it.

Don't bother with software fixes for this case. No registry edit, no command-line trick will fix a dead battery. It's a hardware issue. The only fix is a new battery.

If you're on a laptop, it's trickier. Some laptops have the battery soldered or hidden under the keyboard. Check your service manual. If you can't replace it yourself, take it to a shop. It's a 10-minute job for them.

2. Windows Time Service Stopped or Misconfigured

If the battery is fine (clock keeps correct time while the PC is on, but goes wrong after a reboot where you shut down properly), the Windows Time Service might be the issue. It's the built-in service that syncs your clock with time.microsoft.com or another NTP server.

Here's the quick fix:

1. Press Win + R, type services.msc, hit Enter.
2. Find Windows Time in the list. Double-click it.
3. Set Startup type to Automatic. Click Apply.
4. Click Start to run it now. Then OK.

But that's just the start. The service itself can be corrupted. Run these two commands as Admin (right-click Start > Windows PowerShell (Admin)):

net stop w32time
w32tm /unregister
w32tm /register
net start w32time
w32tm /resync

This resets the time service completely. After that, your clock should sync within a few minutes. If it still doesn't work, check your time zone settings. Go to Settings > Time & Language > Date & Time. Make sure Set time automatically and Set time zone automatically are both on. If they're off, the clock can drift.

Real-world trigger: This happens a lot after a Windows update that messes with the time service. I've seen it on Windows 10 version 21H2 and 22H2. If you just updated, try the commands above first.

3. Dual Boot Systems – Windows and Linux Fighting Over Clock

If you dual boot Windows 10 with Linux (Ubuntu, Mint, etc.), the clock issue is almost always about how each OS handles the hardware clock. Windows uses local time by default. Linux uses UTC. So every time you boot Linux, it changes the BIOS clock to UTC. Then Windows reads that as wrong and resets it.

Fix is simple: tell Linux to use local time too. Run this in Linux terminal:

timedatectl set-local-rtc 1 --adjust-system-clock

Then check with timedatectl. It should show "RTC in local TZ: yes". Reboot into Windows. Clock should stay correct now.

Alternative fix: change Windows to use UTC. I don't recommend it. It requires a registry hack and breaks some old software. Stick with the Linux fix.

Quick Fix Summary

That's it. Start with the battery. It's the most common. If that's fine, hit the time service. If you dual boot, you already know what the fix is. Your clock won't mess up again.