Every antivirus product uses some system resources. The meaningful question is how much it affects your particular hardware, software, workload, and scan schedule. A product that scores well in an independent lab can still behave differently on an older laptop or a gaming desktop with unusual drivers.
This guide explains how to compare protection and performance. It is not a hands-on benchmark and does not rank seven products from our own testing.
Use independent lab results correctly
AV-TEST scores protection, performance, and usability separately. AV-Comparatives publishes dedicated performance tests that measure system impact in defined Windows test conditions. Those results are useful evidence, but they are not a guarantee for every PC; AV-Comparatives explicitly encourages users to try software on their own systems.
When reading a lab result, record the product version, operating system, test date, settings, and category. Do not compare a current product with an old score or treat a performance score as a protection score.
What causes an antivirus slowdown?
- Real-time scanning can add work when files are opened, copied, compiled, or downloaded.
- Scheduled full scans can compete for disk and CPU resources.
- Browser, ransomware, web, email, and behavior modules can add separate checks.
- Updates and cloud lookups can create short network or CPU spikes.
- Conflicts with game launchers, backup tools, developer tools, or hardware utilities can cause unusual behavior.
The right fix may be rescheduling a scan or diagnosing a conflict rather than replacing the entire security product.
Measure your own PC
- Record your OS, CPU, RAM, storage type, GPU, and common workload.
- Before installing or changing security software, record boot-to-desktop time, application launch time, large-file copy time, and a repeatable game or productivity benchmark.
- Repeat each measurement several times with the same background programs and network conditions.
- Compare idle use, real-time protection during normal work, and a scheduled/full scan separately.
- Check Task Manager or Activity Monitor for the process and event causing the spike.
- Test after updates; a new engine or operating-system build can change results.
For Windows Defender, Microsoft documents a performance analyzer that records scan events and reports the files, processes, paths, and extensions contributing to scan time. That is more useful than guessing from a single CPU percentage.
Candidate categories to investigate
Built-in protection. Microsoft Defender is already integrated into supported Windows versions and should be compared using current independent protection and performance results, not the assumption that built-in means “free of overhead.”
Lightweight paid suites. ESET, Bitdefender, and other vendors often appear in independent performance comparisons, but the relevant product version and test date matter more than a longstanding reputation.
Secondary scanners. A second on-demand scanner is not automatically safer. Running multiple real-time engines can create conflicts and extra overhead; follow vendor guidance before enabling overlapping protection.
Gaming and low-end hardware
A “gaming mode” may postpone scans, updates, or notifications, but implementations differ. Verify what the mode actually pauses and whether it applies automatically to your game. On low-end hardware, schedule intensive scans during downtime, keep adequate free storage, and avoid stacking multiple security suites with overlapping real-time features.
Do not disable protection or create broad exclusions simply to raise a frame-rate benchmark. If an exclusion is necessary for a known conflict, narrow it, document it, and understand the security trade-off.
Frequently asked questions
Which antivirus has the lowest CPU usage?
There is no permanent winner. Use the newest AV-TEST or AV-Comparatives performance result for the exact product version, then test it on your PC.
Does Windows Defender slow down gaming?
It can affect some workloads during scans or file activity, but the magnitude varies. Use Microsoft’s performance analyzer or controlled local tests before switching products.
Are cloud-based antivirus engines always faster?
No. Cloud assistance can move some analysis off-device, but network delay, local scanning, updates, and the rest of the suite still affect performance.
The bottom line
Choose antivirus by balancing current protection evidence, independent performance results, compatibility, and your own measurements. “Doesn’t slow down your PC” is not a product attribute that can be guaranteed without conditions. Measure normal use and scan use separately, keep protection enabled, and fix the specific workload or conflict you can actually observe.
Sources and verification notes
These independent-lab and vendor sources were checked on August 1, 2026:
- AV-TEST Windows 11 home-user results
- AV-Comparatives performance test methodology and results
- Microsoft Defender performance analyzer
- Microsoft Defender current test results on AV-TEST
No independent benchmark was run for this article, and no provider’s marketing claim is treated as a universal performance guarantee.