Wi-Fi connects and works, but everything is slow: pages take seconds to load, video buffers, and downloads crawl. Slow Wi-Fi is usually a signal or congestion problem, so the fixes start with measuring the speed and finding where it is lost.
The fix, in order
Measure the speed properly. Run a speed test on the affected device, then run the same test on another device in the same spot, and then next to the router. Comparing the three results shows whether the problem is the device, the location, or the internet service.
Move closer to the router. Distance and walls are the biggest cause of slow Wi-Fi. Test in the same room as the router to see how much speed distance is costing.
Switch to the 5 GHz band. 5 GHz is faster than 2.4 GHz at short range, so use it when you are near the router and 2.4 GHz when you are far away.
Restart the router. A router that has run for weeks can slow down, and a restart clears the temporary state.
Change the Wi-Fi channel. Neighbours' networks on the same channel cause interference. Pick a less busy channel in the router settings, with help from the Wi-Fi channel planner, or let the router choose automatically.
Check what else is using the connection. Cloud backups, game downloads, and video calls on other devices all share the same internet. Pause large downloads and test again.
Be wary of speed test results from a single test. Run the test two or three times, and test at different times of day, before concluding the service is slow.
If it still happens
If the speed is slow on every device even next to the router, test with a wired Ethernet connection. If wired is fast and Wi-Fi is slow, the router's Wi-Fi is the problem. If wired is also slow, the internet service is the problem, so contact the provider.
Common questions
Why is Wi-Fi slow but Ethernet fast? Ethernet does not suffer from distance, walls, or interference, so it shows the true speed of the internet service. If Ethernet is fast and Wi-Fi is slow, the Wi-Fi link itself is the bottleneck.
Does the number of connected devices slow Wi-Fi down? Yes, especially on older routers. Every active device shares the same radio time and the same internet connection, so a house full of streaming and downloading devices will feel slow.