A Wi-Fi extender halves your speed and adds a second network name to argue with. Before you buy one, spend twenty minutes on these. Most dead zones are a placement problem, and placement is free.
1. Move the router
Routers end up where the cable comes in: a basement corner, a closet, behind the TV. Wi-Fi radiates outward and down more than up. Move it to the most central, highest spot you can reach with the existing cable, out in the open, not in a cabinet. This alone fixes a third of the calls we get.
2. Check what is in the way
Stand where the signal is bad and draw a line to the router. Count what it passes through. Brick, stone, concrete, tile floors, mirrors, a fridge, an aquarium, foil-backed insulation, a metal duct. Two or more of those and no amount of power will help; the fix is an access point on the far side of the obstacle.
3. Look at the channel
Your neighbours' networks compete for the same airtime. Most routers pick a channel at boot and never change it. In the router's admin page, set 2.4 GHz to channel 1, 6 or 11 (whichever a free phone analyser app shows is quietest) and let 5 GHz auto-select. If the router is more than five years old, it may be congesting itself.
4. Separate the bands, or stop separating them
Some routers broadcast one name for both 2.4 and 5 GHz and steer devices between them, and do it badly. Some broadcast two names and devices cling to the wrong one. Try the opposite of whatever you have. 5 GHz is faster up close; 2.4 GHz reaches further through walls.
5. Count the devices
Forty connected devices on a consumer router is a load problem, not a coverage problem. Smart plugs, bulbs, speakers, cameras, doorbells, two laptops, four phones, three TVs: it adds up. The symptom is "Wi-Fi is slow everywhere" rather than "slow in one room".
If none of that works
Then you have a real coverage gap, and the answer is a second access point with a cable to it, not an extender. If you genuinely cannot run a cable, a mesh system with a dedicated wireless backhaul band is the next best thing; an extender is the last resort.
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