Fiber speed suddenly dropped in half? What to check

Your fiber connection used to deliver a certain speed, and now a test shows about half. That can point to Wi-Fi or a device limit, but a speed test by itself cannot tell you which part of the connection changed.

Start with a repeatable test, then compare a wired connection with Wi-Fi. The Speed Test measures download speed, upload speed, ping, and jitter, so you can see whether the slowdown affects one direction or the whole connection.

Check the speed in a consistent way

1. Open the Speed Test on a computer connected to your home network. Close large downloads, cloud backups, and video streams on other devices before you run it.
2. Run the test two or three times, about a minute apart. Note the download, upload, ping, and jitter results, and whether they stay close or jump around.
3. If possible, connect the computer to the router with an Ethernet cable and test again. Use a known gigabit-capable port and cable if your plan is faster than 100 Mbps.
4. Compare the wired result with Wi-Fi in the same room as the router. Then compare it with Wi-Fi where you usually notice the slowdown.

Do not connect a computer directly to the fiber terminal or ONT unless your internet provider tells you to. That setup may require provider-specific settings, and the router is often needed for security and network access.

What the result means

Ethernet is close to your usual speed, but Wi-Fi is much slower

The fiber service and router connection are probably working, while the wireless connection is the weaker part. Distance, walls, interference, or the device's Wi-Fi hardware can reduce throughput. If Wi-Fi is slow even next to the router, check the band and router settings before blaming the fiber line.

Ethernet and Wi-Fi are both about half of normal

The issue may be in the router, the fiber terminal, a cable, or the provider's network. If more than one wired device gets the same low result, that is stronger evidence of a shared connection problem than a single slow laptop is.

Download is low, but upload is normal

This can happen when downloads are competing with other traffic, a device or router is limiting downloads, or the provider's route is congested. Check whether another device is downloading or updating, then repeat the test when the network is otherwise idle.

Both directions are inconsistent or ping and jitter are high

The connection may be busy or unstable rather than simply capped at half speed. A speed test is a short sample, so repeat it at different times and note any dropouts or pauses while using the connection.

The result is close to half of a gigabit plan, around 500 Mbps

That result alone does not prove the fiber service is faulty. The computer, Wi-Fi adapter, router, Ethernet port, or cable may be limiting the connection. Also, a gigabit Ethernet link has protocol overhead, so a test will not normally show the full advertised line rate as usable download speed.

How to fix it

1. Pause other network use. Stop streaming, game downloads, cloud backups, and software updates on every device you can. One busy device can use a large share of the connection, especially if it is uploading.
2. Compare over Ethernet. Connect a computer to the router, then run the test again. On Windows 11, check the connection under Settings › Network & internet › Ethernet. On macOS, check the wired service under Apple menu › System Settings › Network. If the computer has no Ethernet port, use a known gigabit-capable adapter.
3. Check the cable and router port. Reseat both ends of the Ethernet cable and try another LAN port. A damaged cable or a port negotiating at 100 Mbps can sharply limit the result. Replace a visibly damaged cable with a good-quality one rated for gigabit Ethernet or faster.
4. Test Wi-Fi close to the router. Move within a few feet, keeping the computer in the same position for each comparison. If the result improves, the problem is likely coverage or interference in the usual location. On Windows 11, review Wi-Fi settings at Settings › Network & internet › Wi-Fi. On macOS, use Apple menu › System Settings › Wi-Fi. Available band and channel options depend on your router and device.
5. Restart the router and fiber terminal. Follow your provider's instructions for powering them off and back on, and allow several minutes for the fiber connection to return. Do not unplug or bend the thin fiber cable, and do not factory-reset equipment as a first step.
6. Check your plan and provider notices. Confirm the current plan speed and look for a service notice or outage. If the wired result remains near half on more than one device, contact the provider with the time of each test, the wired results, and whether the ONT or router showed an alert.

When to contact your provider

Call your provider if multiple wired devices show a similar drop after you have paused other traffic, checked the Ethernet cable and ports, and restarted the equipment as instructed. Ask whether the fiber terminal is reporting an optical signal problem, whether there is local congestion or maintenance, and whether your account's speed profile has changed. Give them the results from several tests rather than one unusually low reading.

If only one computer is slow over Ethernet, try another cable and another device before requesting a line repair. If the router or ONT has a red warning light, repeated connection losses, or a damaged power supply, tell the provider rather than opening the equipment or handling the fiber connector.

The Speed Test exchanges test data with TooLab's server to measure the connection, so results can also vary with network conditions between your home and the test server.