Why is Wi-Fi internet speed slower than cable? A full analysis of the reasons.

You've signed up for a new plan with the promised 300 Mbps, but your Wi-Fi speed barely reaches 50 Mbps, while your cable connection remains at 280 Mbps. Or your internet speed is blazing fast at night, then slumps in the evening. Sound familiar? Slow Wi-Fi affects 8 out of 10 users, and in 95% of cases, it can be resolved without replacing your equipment.

In this article we will look at all possible reasons for the speed drop — from the mundane (the router is in a closet) to the hidden (channel congestion from neighboring networks). You'll learn how to check each factor, what exactly is affecting your network, and What are the router settings? What needs to be changed to restore maximum speed. And at the end, a quick diagnostic checklist and an FAQ with answers to frequently asked questions.

Spoiler: in half the cases, it’s not the router’s fault, but external interference or incorrect device settings. And this is easily fixed!

1. Physical Interference: Why Walls and Microwaves Steal Your Wi-Fi

A Wi-Fi signal is radio waves that weaken when passing through obstacles or encounter interference from other devices. Even if the router is located in the center of the apartment, a thick concrete wall can reduce speed by up to 70%, and a microwave oven can add up to 500 ms of latency.

Here are the main speed thieves in your home:

• 🧱 Walls and partitions: brick, concrete, metal structures weaken the signal by 30-90%. Particularly critical load-bearing walls and reinforced concrete slabs.
• 📡 Neighboring Wi-Fi networks: If there are 10+ networks operating in your range (2.4 or 5 GHz), they create mutual interference. This is called co-channel interference.
• 🍳 Household appliances: microwaves, cordless phones (DECT), baby monitors, wireless speakers operate at a frequency of 2.4 GHz and “clog” the channel.
• 🌲 Plants and aquariumsWater absorbs radio waves extremely well. A large aquarium or indoor fountain can reduce the speed by 15–20%.

How to check? Take a smartphone with the app. Wi-Fi Analyzer (Android) or NetSpot (iOS/macOS) and walk around the apartment. If the signal strength drops below -70 dBm at the place of use, the problem is precisely in physical interference.

⚠️ AttentionIf you live in an apartment building with 15+ networks on a single channel, even the most powerful router won't save you—you'll need to manually configure the channel or change the band to 5 GHz.

2. Incorrect router settings: 5 key parameters

By default, routers are configured with "universal" parameters, which are rarely optimal. For example, channel width 20/40 MHz in the 2.4 GHz range it can automatically narrow to 20 MHz due to interference, which immediately cuts the speed in half.

Check these settings in the router admin panel (usually 192.168.0.1 or 192.168.1.1):

How to change? For routers TP-Link path: Wireless → Wireless Settings. For ASUS: Wireless Network → GeneralOn . Keenetic search in Wi-Fi network → Access point.

3. Network congestion: why is the internet slow in the evening?

Your Wi-Fi speed may be slowing down not because of your router, but because of provider channel congestion or your local network. In the evening, when all the neighbors are watching Netflix in 4K, and you're trying to download a file, your speed can drop by 5-10 times.

How do you know the problem isn't you?

• 📊 Check your cable speed (connect your PC directly to the router). If it's also low, your ISP is to blame.
• 🕒 Run a speed test (Speedtest.net) at different times of the day. If it's 200 Mbps during the day and 20 in the evening, that's peak load.
• 📡 See how many devices are connected to your Wi-Fi. Every smartphone, smart light bulb, or TV eats up some of your bandwidth.

Critical information: If you have a plan with a shared bandwidth (e.g., "up to 300 Mbps for 10 subscribers"), your actual speed may drop to 10–15 Mbps in the evening. This is normal, but your provider is required to provide notice of this in your contract.

⚠️ Attention: Some providers artificially limit the speed of Wi-Fi through PPPoE sessions or VLAN tags. Check if the “Limit Wi-Fi speed” box is checked in the router settings (it happens on Zyxel And D-Link).

Call your provider's support team and check peak loads|

Try changing DNS (for example, to Google: 8.8.8.8)|

Disable background updates on devices|

Reboot your router (sometimes helps when your session freezes) -->

4. Outdated equipment: when the router or device can't handle the speed

If your router was released before 2018, it most likely does not support modern standards. Wi-Fi 5 (802.11ac) or Wi-Fi 6 (802.11ax)Maximum speed for Wi-Fi 4 (802.11n) — 150–300 Mbit/s, but in practice rarely exceeds 100 Mbit/s due to interference.

Check the specifications of your router and devices:

• 📋 Router: the model must support 802.11ac (for 5 GHz) or 802.11ax (for maximum speed). For example, TP-Link Archer C6 or ASUS RT-AX55.
• 📱 Devices: smartphones older than 2019 (eg. iPhone 8 or Samsung Galaxy S8) do not support Wi-Fi 6 and limited to 400–800 Mbps.
• 🖥️ PC Wi-Fi adapter: Built-in adapters in laptops are often weaker than external ones. For example, Intel AX200 will give 2.4 Gbps, and the old one Realtek RTL8188EE — only 150 Mbps.

How do I find out the capabilities of my adapter? In Windows, open Device Manager → Network Adapters and find the model. Then check its specifications on the manufacturer's website.

netsh wlan show interfaces

5. Malware and background processes: who's stealing your traffic

If the speed drops even with minimal load, check if your device has become part of botnet or whether it's infected with a virus that consumes bandwidth. For example, a Trojan. Mirai uses infected routers for DDoS attacks, and mining scripts can "eat up" up to 50% of the channel.

Signs of infection:

• 🔍 The router gets very hot without load.
• 📉 Speed ​​drops to 0–5 Mbps on all devices.
• 🔄 In the router logs (System log) suspicious IP addresses appear (for example, from China or Eastern Europe).
• 📡 Unknown devices in the list of connected clients (DHCP clients).

How to check?

1. Go to the router admin panel and look at the list of connected devices (Wireless Mode → Client List or LAN → DHCP).
2. Check network activity on your PC via Task Manager → Network Adapter (Windows) or Activity Monitor → Network (macOS).
3. Scan your network for open ports using Angry IP Scanner or Fing.

⚠️ Attention: if the list of DHCP clients contains devices with names like android-123456 or unknown, change your Wi-Fi password and router firmware immediately. This is a sign of a hack.

6. Provider settings: restrictions you don't notice

Sometimes the problem lies in hidden provider restrictionsthat you don't know about. For example:

• 📶 Wi-Fi restriction: Some tariffs (especially mobile 4G/5G) artificially limit the speed when distributing through a router.
• 🔄 DPI (Deep Packet Inspection): Your ISP may slow down torrents, 4K videos, or online games.
• 🔒 MAC address binding: If you changed your router but did not tell your ISP its new MAC address, your speed may be limited.
• 📡 Incorrect connection type: for example, instead of PPPoE configured DHCP, due to which the speed is “cut”.

How to check?

1. Connect your PC directly to the ISP cable (without a router) and run SpeedtestIf the speed is high, the problem is with the router or its settings.
2. Call support and ask if there are any restrictions Wi-Fi, MAC address or type of traffic.
3. Check the connection type in the router: for most providers (Rostelecom, Beeline, MTS) you need to set PPPoE with login/password.

7. Router firmware and hardware failures

Outdated router firmware may contain bugs that cause speed drops by 30-70%. For example, in TP-Link Archer C20 firmware versions up to 1.0.12 There was a bug with the 5 GHz speed limitation to 200 Mbps instead of 867 Mbps.

How to update firmware?

1. Find out the router model (written on the sticker at the bottom).
2. Download the latest firmware from the official website (tp-link.com, asus.com etc.).
3. Log into your router's admin panel (192.168.0.1) and find the section System Tools → Firmware Update.
4. Download the firmware file and wait for the reboot (3-5 minutes).

Warning: Do not turn off the router during the update. — this could brick it. If the speed isn't restored after the update, try resetting the settings to factory settings (Reset button for 10 seconds).

Hardware failures are less common, but are also possible:

• 🔥 Chip overheating due to dust or poor ventilation.
• 🔌 Faulty power supply (the router works, but is glitchy).
• 📡 Damaged antenna (for example, after a fall).

Checklist: What to do if your Wi-Fi is slow

Before you call your ISP or buy a new router, go through this list:

Check your cable speed (if it's low, it's your provider's problem)|

Reboot your router (unplug it from the power outlet for 30 seconds)|

Change your Wi-Fi channel to 1, 6, or 11 (2.4 GHz) or 36–48 (5 GHz)|

Update your router firmware to the latest version|

Disconnect all devices from Wi-Fi and test the speed on one PC|

Change the location of the router (raise it higher, move it away from the walls)|

Check the list of connected devices for unknown MAC addresses|

Reset your router to factory settings and set it up again-->

FAQ: Answers to frequently asked questions