Windows Defender Uses Too Many Resources: How to Optimise It
How to reduce its impact without turning it off or losing protection — CPU limit, priority and scan schedule.
Windows' built-in antivirus (Windows Defender) can end up using a lot of CPU during its scans, especially on machines with limited resources. First, an important clarification: the solution isn't turning it off — there are several ways to reduce its consumption without leaving your machine unprotected.
Limit the CPU percentage it can use
Open PowerShell as administrator and run:
Set-MpPreference -ScanAvgCPULoadFactor 30
This limits the scan to a maximum of 30% CPU (you can adjust the number). We don't recommend going below 15% — with less, the scan becomes so slow it might not complete properly.
Change the scan's priority
Set-MpPreference -EnableLowCpuPriority $true
With this, Windows Defender yields to your active programs when both compete for CPU, instead of fighting over it with equal priority.
Schedule the scan for when you won't notice it
Windows Defender → Settings → Scan options → schedule the full scan for a time you don't usually use the computer (overnight, for example). Our guide on how to schedule an automatic scan with Windows Defender covers this step by step.
Exclude folders you already know are safe
If you have very large folders you're certain are safe (a library of your own projects, for example), excluding them from the scan reduces the workload. We cover this with the necessary precautions in how to exclude a safe folder from the Windows Defender scan.
Warning: you'll find guides recommending turning off Windows Defender entirely (via registry or group policy) as a solution. Don't do that unless you already have another antivirus installed and active in its place — being left with no active antivirus at all is a real risk, not just a way to save resources.
If none of this is enough
The problem might not be Windows Defender itself, but that it's competing with another security program installed at the same time. Check that you don't have two antiviruses active simultaneously — that does cause excessive consumption and genuine conflicts between them.
Frequently asked questions
Is it safe to limit the CPU Windows Defender uses?
Yes, within reasonable limits (don't go below 15%). It only makes the scan take a bit longer to complete, it doesn't reduce the quality of detection itself.
Should I uninstall Windows Defender and use another antivirus?
Not necessary just for resource use — with the adjustments in this guide, most cases are solved while keeping protection active. Switching antivirus is a separate decision, not a required solution to this specific problem.
Why is consumption sometimes much higher than other times?
High consumption usually coincides with the periodic full scan or with the virus definitions update, both one-off processes — it isn't constant consumption throughout the day.