Why does my AT&T internet get so slow late at night?

First, try to separate a Wi-Fi problem from a problem with the internet connection. Run a speed test during the day and again when things slow down, preferably on more than one device. Note the download speed, upload speed and latency.

If you can temporarily connect a laptop by Ethernet near the router, test that at the same time as Wi-Fi. Good wired results but bad Wi-Fi results point toward the wireless connection. If both are slow, the router or the connection to AT&T becomes more suspect.

Wi-Fi interference is a possibility, especially if nearby networks or other devices get busier at night. Distance and walls can also make an already weak signal more troublesome.

Try testing close to the router when the slowdown happens. A Wi-Fi analyzer can show nearby networks and channel congestion, which may help you decide whether changing the router's wireless channel is worth trying.

Check what else is using the connection at home. A large download, backup or stream on another device can eat bandwidth and make gaming feel awful. Look at the router's connected-device or traffic information if it provides that, or ask others whether anything heavy is running overnight.

It could also be congestion on the provider's network, but the time of day alone doesn't prove that. If multiple devices are slow and a wired test is slow too, keep a few test results with their times and contact AT&T. That gives support something more useful than just saying the connection is bad at night.