Why is my Wi-Fi slow upstairs?
Because the signal has to pass through a floor and several walls before it reaches you, your device connects at a low data rate even though the internet service is fine. The fix is an access point on that floor — ideally with an Ethernet cable back to your router.
What is actually happening
Wi-Fi speed drops with signal quality. A device two floors from the router negotiates a much slower rate, so a connection that shows two bars may deliver a fraction of your plan.
Devices also hold onto a weak connection rather than switching to a better one, which is why walking upstairs and staying slow is so common.
The 5 GHz and 6 GHz bands that carry the fast speeds have the worst range through floors — so the closer you get to the limit, the more the speed collapses.
What does not fix it
A faster internet plan. The bottleneck is between your device and the router, not upstream.
A more powerful router. Transmit power is regulated and your device's antenna is the weaker side of the conversation anyway.
A plug-in extender in the hallway. It repeats a weak signal and typically halves throughput on every hop.
What does fix it
An access point on the upper floor, wired with Ethernet from below. If a cable pathway exists, this is a same-day improvement that is usually dramatic.
If no cable can reach, a mesh node placed with clear line of sight to the main unit — not tucked in a far corner — is the next best option.