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How to Reduce CPU Usage During a Microsoft Defender Full Scan

Amos Gikunda Oct 10, 2026 870 views

Question details

The user needs to lower the CPU resources consumed by Microsoft Defender during scheduled full scans and is seeking advice on configuring exclusions.

How to Reduce CPU Usage During a Microsoft Defender Full Scan

Product: Microsoft Defender
Device & OS: Windows
Scenario: Running a scheduled Microsoft Defender full scan while trying to manage system resource consumption.
Observed behavior: Microsoft Defender consumes 60% to 80% CPU even though the ScanAvgCPULoadFactor policy is set to a limit of 50.

Before you start

Ensure you are logged into your Windows computer with an administrator account, as executing PowerShell commands and modifying Microsoft Defender policies require administrative privileges.

Solution 1Recommended

Configure CPU Load Factor via PowerShell

Manually enforce the CPU load limit using Windows PowerShell to ensure your system policy is correctly applied to Microsoft Defender.

The ScanAvgCPULoadFactor policy limits the average CPU usage of Microsoft Defender. Even with this applied, high CPU usage can occasionally be normal depending on the file types being processed.

Open PowerShell as Administrator

Right-click the Start menu button and select 'Windows PowerShell (Admin)' or 'Windows Terminal (Admin)' from the context menu.

Execute the CPU Limit Command

Type the command 'Set-MpPreference -ScanAvgCPULoadFactor 50' and press Enter. You can adjust the numerical value between 5 and 100 based on your specific resource needs.

Verify the Configuration

Run the command 'Get-MpPreference | Select-Object ScanAvgCPULoadFactor' to confirm that the value has been successfully updated in your system.

Configure CPU Load Factor via PowerShell

Average vs Maximum Limit: This policy restricts the average CPU usage over time, not an absolute maximum. Temporary CPU spikes during a full scan are completely normal.

Solution 2

Schedule Full Scans Outside Working Hours

Shift the intensive full scan process to times when the computer is not actively being used by the user.

Solution 3

Manage Exclusions and Software Conflicts

Prevent conflicts with other background software and carefully manage exclusions to optimize scan performance without compromising security.

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Frequently Asked Questions

Why does Microsoft Defender ignore my ScanAvgCPULoadFactor setting?

The ScanAvgCPULoadFactor setting restricts average CPU usage over the duration of the scan, not absolute maximums. Defender may temporarily spike above this limit when unpacking large archives or scanning complex files.

Should I add file exclusions to Microsoft Defender to speed up my full scan?

Microsoft strongly advises against adding exclusions unless absolutely necessary and only for completely trusted locations. Exclusions create security blind spots that malware can exploit, significantly reducing your device's protection.

What should I do if my CPU usage remains unusually high despite policy changes?

First, ensure your Windows operating system and Defender definitions are fully updated. If the issue persists, collect your system's diagnostic logs and contact Microsoft Support to investigate deeper software conflicts or system errors.

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