Why does Wi-Fi internet speed drop when downloading? And how to fix it.

Are you downloading a file over Wi-Fi, but your speed suddenly drops from 100 Mbps to 5-10, or even drops completely? This problem is familiar to many, especially those with inexpensive routers or those living in densely populated apartment buildings. In this article, we'll look into it. 7 Key Reasons, why this happens, and we will give concrete solutions — from changing router settings to upgrading equipment.

It's important to understand that a drop in download speed isn't always the provider's fault. More often than not, the problem lies in network settings, channel congestion or hardware limitations your router. We won't recommend "just rebooting the router" (although that sometimes helps), but will focus on deep diagnostics and methods that really work.

First, check: is the problem occurring on just one device or on all? If the speed drops on both your smartphone and laptop, the router or network is to blame. If it's only on your PC, it could be a Windows setting or Wi-Fi adapter driver issue. We'll look at each scenario separately below.

1. Wi-Fi channel overload by neighboring networks

In apartment buildings, one of the most common reasons for speed drops is congested radio channelsIf there are 20-30 Wi-Fi networks around you operating on the same channel (for example, 6th or 11th in the 2.4 GHz range), they create interference, and the speed "sags" under load.

How to check? Use free utilities like Wi-Fi Analyzer (Android) or NetSpot (Windows/macOS). They will show which channels are busy. If your router is on the same channel as 5-10 of its neighbors, that's the cause of the slowdown.

  • 📡 Solution 1: Manually change the Wi-Fi channel in your router settings. For 2.4 GHz, choose the least crowded channel. 1, 6 or 11 (they do not overlap). For 5 GHz - any channel marked DFS (if your router supports it).
  • 🔄 Solution 2: Turn on the function Auto Channel Selection (If it's available in the firmware). The router will automatically select the least congested channel.
  • 🚫 Solution 3: Disable support for legacy standards 802.11b/g in your wireless network settings. They slow down the entire network, even if you have modern devices connected.
📊 Which Wi-Fi band do you use most often?
2.4 GHz only
5 GHz only
Both ranges
Don't know
⚠️ Attention: Channels 12–14 Radios in the 2.4 GHz band are officially banned in Russia and some other countries. Their use may lead to legal conflicts or network instability.

2. Router bandwidth limitations

Cheap routers (especially models released before 2020) often have hardware limitations for traffic processing. For example, the processor can't handle the large number of packets when downloading torrents or large files, and the speed is throttled to 20–30% of the maximum.

How does this manifest itself? During normal surfing, the speed is stable, but as soon as you start downloading a file, it drops by 3-5 times. This is especially noticeable on routers with chips. Realtek RTL818x or Mediatek MT7620.

Router model Max. Wi-Fi speed (theoretical) Actual speed under load Reason for restriction
TP-Link TL-WR841N 300 Mbps 50–80 Mbps Weak processor (560 MHz)
D-Link DIR-615 300 Mbps 40–60 Mbps 16 MB of RAM
Asus RT-N12 300 Mbps 70–100 Mbps Outdated firmware
Xiaomi Mi Router 3G 300 Mbps 120–150 Mbps Software restriction (artificial)

What to do?

  • 🔧 Update the firmware Upgrade your router to the latest version. Sometimes manufacturers optimize traffic processing.
  • ⚙️ Disable QoS (Quality of Service) in the settings, if enabled. This feature can artificially limit speed to prioritize traffic.
  • 💻 Check CPU load router via Telnet/SSH (if supported). Commands: 
    top

    cat /proc/cpuinfo

    If the processor load is close to 100%, the router can't cope.

3. How Windows settings affect Wi-Fi speed

Even if the router is powerful and the channel is free, operating system settings may artificially limit speed. There are several pitfalls in Windows 10/11:

  1. TCP/IP Autoconfiguration - sometimes resets parameters to default values, which are not optimal for high-speed networks.
  2. Wi-Fi adapter power saving — reduces signal strength to save battery (relevant for laptops).
  3. Bandwidth limitation - can be installed by third-party programs (for example, download managers).

How to check and fix:

  1. Open Control Panel → Network and Internet → Network and Sharing Center → Change adapter settings.
  2. Right-click on your Wi-Fi connection → Properties → Configure → Advanced.
  3. Check the parameters:
    • 802.11n Wireless Mode → Install Auto or 802.11n Only.
    • Transmit Power → Exhibit Highest (maximum power).
    • Roaming Aggressiveness → Install Lowest (to avoid constant reconnections).

☑️ Optimizing Wi-Fi in Windows

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⚠️ Attention: If you are using a VPN or proxy server, your download speed may drop due to traffic encryptionDisable your VPN and test your speed without it. Some services (for example, NordVPN or ProtonVPN) limit the speed on free tariffs.

4. Problems with Wi-Fi adapter drivers

Outdated or faulty drivers are one of the most insidious causes of slow internet speeds. Symptoms:

  • The speed is stable for the first 5-10 minutes, then drops sharply.
  • IN Device Manager There is an exclamation mark next to the adapter.
  • After restarting the PC, the speed is temporarily restored.

How to diagnose:

  1. Open device Manager (Win + X → Device Manager).
  2. Expand the tab Network adapters and find your Wi-Fi module (for example, Intel Wireless-AC 9560 or Qualcomm Atheros QCA61x4).
  3. Check the driver version: right-click → Properties → Driver.

Solutions:

  • 🔄 Update your driver through the manufacturer's official website (not through Windows Update!). For adapters Intel, Qualcomm or Realtek Download drivers only from websites intel.com, qualcomm.com or realtek.com.
  • 🗑️ Remove the old driver completely by using Display Driver Uninstaller (DDU), then install a new one.
  • ⚡ Roll back to the old versionIf the problem appeared after an update, in the adapter properties, click Roll back.
How can I find out the model of my Wi-Fi adapter if it is not recognized by the system?

Open Command Prompt (Win + R → cmd) and enter: 

wmic nic get name, manufacturer, speed, netconnectionid

Or use the utility HWiNFO for detailed diagnostics.

5. External interference: microwaves, Bluetooth, and walls

The 2.4 GHz band, which is used by most Wi-Fi networks, extremely sensitive to interferenceSources of problems:

  • 🍳 Microwave ovens — operate at a frequency of 2.45 GHz, completely blocking Wi-Fi during warm-up.
  • 📱 Bluetooth devices (headphones, speakers, mice) - use the same range.
  • 🧱 Walls and furniture — concrete, metal and even aquariums weaken the signal.
  • 🚗 Neighboring Wi-Fi networks - especially if they operate at high power.

How to deal with interference:

  • 📶 Switch to 5 GHz - This range is less susceptible to interference, but has a shorter range.
  • 🔌 Change the location of the routerOptimally, at a height of 1–1.5 m, in the center of the apartment, away from household appliances.
  • 🛡️ Use Mesh systems (For example, TP-Link Deco or Asus ZenWiFi), if the area of ​​the house is more than 100 m².

6. Provider restrictions (Throttling)

Some internet providers artificially slow down at:

  • 📥 Downloading torrents (P2P traffic).
  • 🎮 Online games (to reduce ping for other subscribers).
  • 📺 Streaming video (Netflix, YouTube in 4K).

How to check if there is throttling:

  1. Run a speed test on speedtest.net — write down the result.
  2. Start downloading a large file (for example, a Linux image from ubuntu.com).
  3. Run it again in parallel speedtestIf the speed has dropped by 2-3 times, your ISP is most likely throttling your traffic.

What to do?

  • 📞 Call support and check if there are any restrictions on your plan. Sometimes throttling kicks in after exceeding monthly traffic limit (e.g. 1 TB).
  • 🔒 Use a VPN (For example, WireGuard or OpenVPN). Some providers do not limit encrypted traffic.
  • ⏳ Download files at night — many providers lift restrictions from 2:00 to 8:00.
⚠️ Attention: Throttling conditions may vary depending on your plan and region. Please check your personal account or contact your operator for the latest information.

7. Incorrect MTU and packet fragmentation settings

MTU (Maximum Transmission Unit) — is the maximum size of a data packet that can be transmitted without fragmentation. If the MTU value is too high, packets are "cut" into pieces, which leads to loss of speed and increased ping.

The optimal MTU value for most networks is 1500 byte. But if you have a PPPoE connection, it should be 1472 (due to protocol headers). How to check and change:

  1. Open Command Prompt (Win + R → cmd).
  2. Enter: 
    ping -f -l 1472 ya.ru

    If packets are fragmented, reduce the number (1468, 1464 etc.) until you receive a response without fragmentation.

  3. Set the found MTU value in the router settings or via the command: 
    netsh interface ipv4 set subinterface "Connection_Name" mtu=1472 store=persistent

FAQ: Frequently asked questions about slow Wi-Fi

Why does the speed drop only at night?

This is most likely due to overload of the provider's network — in the evening and at night, many users actively download files, watch high-definition videos, or play online. It is also possible automatic download of updates on devices (Windows, smartphones, game consoles) that are "eating up" bandwidth. Check if scheduled updates are enabled.

Can antivirus software affect Wi-Fi speed?

Yes, some antiviruses (for example, Kaspersky Internet Security or Avast) scan all incoming traffic, which can slow down file downloads. Disable the "Network Scan" feature or add an exception for your browser/download manager. Also, check if your antivirus is blocking it. ports, used for downloading (for example, 80, 443, 6881–6889 for torrents).

Why is the speed normal on the phone, but not on the PC?

This is a typical situation where the problem lies in PC settings:

  • Outdated Wi-Fi adapter driver (update via device Manager).
  • Speed ​​limit in adapter settings (check the parameter Link Speed V Properties → Advanced).
  • Background programs that consume traffic (torrent clients, cloud synchronizers like Google Drive or Dropbox).
  • Viruses or mining scripts running in the background (check Task Manager (for suspicious processes).

Will replacing the router with a more expensive one help?

In 80% of cases - Yes, but only if:

  • Your current router is older than 5 years or belongs to the budget segment (for example, TP-Link TL-WR740N, D-Link DIR-300).
  • You are using a tariff with speed above 100 Mbps, and the router only supports 100 Mbps on LAN ports.
  • You have a lot of devices (10+) connected simultaneously - cheap routers can't handle such a load.

Recommended replacement models (2023–2026): Asus RT-AX88U (for gamers), TP-Link Archer AX6000 (for large houses), Xiaomi AX3600 (optimal price/quality ratio).

How can I check who else is using my Wi-Fi?

If your speed is slowing down due to "foreign" devices connected to your network:

  1. Go to the router's web interface (usually 192.168.0.1 or 192.168.1.1).
  2. Find the section DHCP Clients List, Connected Devices or Local area network.
  3. Check the list of connected devices. Unknown MAC addresses indicate a hack.
  4. Change your Wi-Fi password to a more complex one (at least 12 characters, with numbers and special characters) and enable encryption WPA3 (if supported).

📖 Read also

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