Step 1: Is it everything or one device?
If only one device is slow, the problem is that device, its Wi-Fi adapter or its software. If everything is slow, keep going.
Step 2: Test at the router
Connect a device to the router with Ethernet, pause other devices and run a WiFi Ping test. This shows what your line delivers at its best.
- Close to your plan: the line is fine, so look at Wi-Fi coverage and interference
- Far below your plan: restart the modem and router, then test again
- Still low: note the time and contact your provider with your saved results
Step 3: Check responsiveness under load
If speeds look fine but everything lags when someone downloads, the loaded latency reading will show a big jump. That is bufferbloat, and a router setting can usually fix it.
Step 4: Look for patterns
Save tests through the day. Consistently slow evenings point to congestion on your provider's network. Random slowdowns point to Wi-Fi interference or a faulty device.
Common culprits
Background updates and cloud backups, too many devices, an old router, weak Wi-Fi signal, a VPN, damaged cables, and providers throttling or oversubscribing a local network.