Set Maximum CPU Usage for Windows Defender Scan

This guide shows you how to limit the CPU usage that Windows Defender (Microsoft Defender Antivirus) uses during a scan. By default, Defender can use a large portion of your processor, which can slow down other tasks. Setting a maximum CPU usage percentage helps keep your system responsive while scans run in the background. You’ll need to use PowerShell as an administrator, but no other special tools are required.

What You’ll Need

• Windows 10 or Windows 11 (Pro, Enterprise, or Education editions – the setting is not available on Home edition).
• Administrator access to run PowerShell as an administrator.

Step-by-Step

1. Open PowerShell as Administrator. Click the Start button, type PowerShell, right-click on “Windows PowerShell” and select “Run as administrator.” If prompted by User Account Control, click “Yes.”
2. Check the current CPU limit (optional). Run the following command to see the current setting: Get-MpPreference | Select-Object -Property ScanAvgCPULoadFactor. The default is usually 50 (which means 50%).
3. Set the maximum CPU load percentage. Use the command below, replacing 30 with your desired percentage (between 5 and 100): Set-MpPreference -ScanAvgCPULoadFactor 30. This sets the maximum CPU usage that Defender will use during scans to 30%.
4. Verify the change. Run the same command as in step 2 to confirm the new value is applied. You should see the number you set.
5. Close PowerShell. The setting is saved immediately and will apply to future scans. You don’t need to restart your computer.

Common Mistakes

• Using the Home edition of Windows. The Set-MpPreference cmdlet with the ScanAvgCPULoadFactor parameter is not supported on Windows Home. You may get an error or the setting may not stick. Upgrade to Pro or use a different method (like Group Policy) if you need this feature.
• Setting the value too low. A value below 5% may cause scans to take extremely long or appear to hang. Microsoft recommends a minimum of 5%.
• Setting it to 100%. This effectively removes the limit, which defeats the purpose. It can also cause system slowdowns during scans.
• Not running PowerShell as administrator. If you run the command without admin rights, you’ll get an “Access denied” error. Always right-click and choose “Run as administrator.”
• Forgetting to verify. After setting, always check that the value was applied. Sometimes a policy (like Group Policy) overrides your manual setting.

Tips

• Choose a balanced value. A setting between 20% and 50% is usually good. It keeps scans from hogging your CPU while still finishing in a reasonable time.
• Use Group Policy for more control (Pro/Enterprise). If you need to enforce this setting across multiple devices, use the Group Policy Management Console: Computer Configuration → Administrative Templates → Windows Components → Microsoft Defender Antivirus → Scan → “Specify the maximum percentage of CPU utilization during a scan.” Enable it and set the percentage.
• Monitor during scans. Open Task Manager (Ctrl+Shift+Esc) and look at the CPU usage of “Antimalware Service Executable” (MsMpEng.exe) during a scan to see if it stays near your limit.
• Schedule scans during idle times. Even with a CPU limit, scans can still use disk I/O. Schedule scans for when you’re not using the computer heavily.

Troubleshooting

• The command returns an error. If you see an error like “The term ‘Set-MpPreference’ is not recognized,” make sure you’re in PowerShell (not Command Prompt) and that you have the Defender module loaded. If you’re on Windows Home, this is likely the cause – the cmdlet is not available.
• The setting doesn’t stick after a reboot. This can happen if a Group Policy is overriding your setting. Check with your IT administrator, or run gpupdate /force in an elevated command prompt to refresh policies. If a policy is defined, it will overwrite your manual value.
• Defender still uses more CPU than the set limit. The ScanAvgCPULoadFactor is a target, not a hard cap. It adjusts the scan’s CPU usage based on system activity. If the system is idle, Defender may use more CPU to finish faster. This is normal. If you need a hard cap, consider using a third-party antivirus or adjusting the scan schedule.
• You can’t find the setting in Group Policy. Make sure you’re looking in the correct path: Computer Configuration → Administrative Templates → Windows Components → Microsoft Defender Antivirus → Scan. If you don’t see it, your Windows version may not have this policy (it’s available in Windows 10/11 Pro and Enterprise).
• After changing the setting, scans run slower than expected. That’s the trade-off. If scans take too long, increase the percentage gradually (e.g., from 30% to 50%) until you find a balance.

Frequently Asked Questions

Does this setting affect real-time protection?

No, ScanAvgCPULoadFactor only applies to scheduled and manual scans. Real-time protection uses a different mechanism and is not limited by this setting.

Can I set the CPU limit to 0%?

No, the minimum allowed value is 5%. Setting it to 0 will likely cause an error or be ignored.

Will this make my computer faster?

It can make your computer feel more responsive during scans, because the CPU is not fully occupied by Defender. However, scans may take longer to complete.

How do I revert to the default setting?

Run Set-MpPreference -ScanAvgCPULoadFactor 50 to set it back to the default 50%.

Is this setting available on Windows 10 Home?

No, it is only available on Pro, Enterprise, and Education editions. Home users cannot change this setting via PowerShell or Group Policy.

Does this also limit disk usage during scans?

No, this setting only controls CPU usage. Disk I/O is managed separately and is not affected.

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