Why is my WiFi slower than the plan speed?

The answer

Your WiFi can be slower than the plan figure because of distance from the router, walls, interference from neighbouring networks, older devices that support only slower WiFi standards and many users sharing the capacity at once. Network overhead and limits at the website's end also reduce results. To find the cause, test with a cable from a laptop to the router, then repeat on WiFi in your usual room, at different times of day. The gap shows whether the line or the home network is responsible.