Does Avast Slow Down Your Computer? What the Lab Tests Actually Show

Short answer: for most people, no — not in any way you would notice day to day. Independent lab AV-TEST measures exactly this, and Avast’s performance scores in its 2025 test rounds sat between 5.5 and a perfect 6 out of 6. There are real exceptions — full scans, very old hardware, and the first days after installation — and this page covers those honestly, with the measured data behind each claim.

How AV-TEST Measures Slowdown

AV-TEST, the German independent lab, scores every antivirus on Performance using the same routine on reference PCs: launching popular websites, downloading frequently used applications, launching standard software, installing programs, and copying thousands of files locally and over a network. The product’s times are compared against the same tasks with no antivirus. A score of 6/6 means top-tier — impact at or better than the industry norm. It is the fairest like-for-like slowdown data that exists, which is why this page leans on it instead of opinion.

Avast’s Actual Performance Scores

• AV-TEST, September–October 2025 (Windows 11, Avast Free): Performance 5.5/6 — with a perfect 6/6 for protection and 6/6 for usability in the same test. The half-point deduction reflects small slowdowns spread across everyday tasks, not one big problem.
• AV-TEST, April 2025: Performance 6/6. In that round Avast Free earned a flawless Top Product result across protection, performance, and usability.
• AV-Comparatives’ Performance Test has likewise rated Avast Advanced+, its highest band, for system-speed impact.

Within the detailed measurements, the pattern is consistent: the tasks where Avast costs you time are measured in tiny percentages. In one recent AV-TEST round, launching popular websites ran about 3% slower than the industry average — a fraction of a second on a page load. File copying, downloads, and installations all sat at or near the industry norm. Antivirus software that scores 5.5–6 in this test is not the reason a healthy PC feels slow.

Why Your PC Might Still Feel Slow With Avast

Lab scores describe a healthy machine on default settings. If Avast feels heavy on your computer, it is usually one of these four things:

1. A full scan is running

Every antivirus — Avast included — uses serious CPU and disk while running a full system scan. A machine that feels fine at idle can stutter mid-scan, especially while launching apps or games. This is normal behaviour, not a flaw, and it ends when the scan ends. Schedule full scans for times you are not using the machine, and use Do Not Disturb Mode (which Avast enables automatically for full-screen apps and games) to stop scans and alerts interrupting play.

2. The first days after installing

Right after installation, Avast builds its picture of your system: first full scan, software inventory, reputation checks on your programs. This settling-in period makes almost any new antivirus feel heavier than it will a week later.

3. Low RAM or an old hard drive

On a machine with 8GB of RAM or less — or worse, a spinning hard drive — every background service competes for scarce resources, and an antivirus with several shields is one of the bigger residents. The labs’ “standard PC” is more generous than a ten-year-old laptop. If your machine is in this class, the fix is a lighter configuration, not no protection: turn off optional shields you don’t use and let the core File, Behaviour, and Web shields do the work.

4. Two antiviruses at once

Running Avast alongside another real-time antivirus (including a leftover trial of a rival, or Microsoft Defender left in active rather than passive mode) causes both to scan everything twice. The resulting slowdown gets blamed on whichever one you installed last. Avast automatically puts Defender into passive mode on a correct install — if it didn’t, that conflict is the first thing to check.

How to Make Avast Lighter: Settings That Help

• Keep Smart Scan, drop the extras: use the quick Smart Scan weekly instead of daily full scans.
• Use Do Not Disturb Mode for gaming and presentations; it silences scans and pop-ups while a full-screen app runs.
• Trim optional shields: if you never use it, the Sandbox, data-shredder prompts, and add-on tools (Cleanup, Driver Updater) are upsells, not protection — decline or disable them.
• Uninstall the browser extensions you don’t use. Web protection lives in the main shields as well; duplicate extensions add browser overhead for little gain.
• Reboot after big updates — a pending-reboot state after a program update is a classic cause of a temporarily sluggish machine.

How Avast Compares on Performance

Avast’s 5.5–6 performance band puts it level with most top-scoring rivals — TotalAV, for instance, scored 6/6 for performance in most of its 2025–2026 AV-TEST rounds with a 5.5 in one. The differences between the leading products in the lab’s performance test are small enough that no major brand wins or loses a purchase decision on speed alone. Where slowdown genuinely decides things is on old, low-memory hardware — and there, a lean configuration matters more than the brand on the box.

One related component worth knowing about: Avast’s paid tiers add a configurable firewall and network tools on top of these shields, and connection filtering adds almost no overhead of its own. We reviewed that component separately: Avast Firewall review.

Test It Yourself in Ten Minutes

You don’t have to take the labs’ word for it. To feel Avast’s impact on your own machine:

1. Baseline: reboot, wait five minutes for startup to settle, then open Task Manager and note the idle CPU (a healthy modern PC sits at 1–5%).
2. Time a routine task: open your usual set of browser tabs and three everyday programs, and time it. Then time copying a large folder (a few GB of photos works well) to another location.
3. Repeat with Avast fully active (it already is, if installed) — and, for contrast, with its shields paused for ten minutes via the system-tray menu (right-click the Avast icon, “Avast shields control”). Avast will warn you; that is fine for a ten-minute test, and protection resumes automatically.
4. Compare honestly. If the numbers are within a few seconds of each other, Avast is not your slowdown. If one task is dramatically slower with shields on, note which — file copying points to File Shield scanning on a very full or slow disk; slow program launches on an old machine point to reputation checks on first run.

This test measures your hardware, which no lab score can — and it usually ends with the real culprit (a dying hard drive, 40 startup programs, 96% full storage) exposing itself in Task Manager instead.

When Switching Antivirus Actually Makes Sense

Given how close the top products’ performance scores are, switching brands rarely cures a slow PC. It is worth considering only when: your machine has 4GB of RAM or a spinning hard drive and you have already trimmed Avast’s optional features; you confirm with the test above that one specific Avast behaviour (usually scanning during your working hours) is the bottleneck and scheduling can’t move it; or you are leaving Avast for non-performance reasons anyway — pricing, features, or support — and want the new product to be no heavier. In that case, judge replacements by the same AV-TEST and AV-Comparatives performance data used on this page, not by “lightweight” marketing claims, which every vendor makes and only the labs verify.

The Bottom Line

Does Avast slow down your computer? On a reasonably modern PC, the measured answer is barely, and mostly during scans — AV-TEST performance scores of 5.5–6 out of 6 across 2025 back that up. If your machine feels slow with Avast installed, work through the four causes above before blaming the antivirus: in our experience the culprit is usually a scan schedule, a second antivirus, or hardware that was already struggling.

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