Why does my wireless mouse lag?

Low battery, the receiver far away or behind the PC, or interference from USB 3 ports and Wi-Fi.

Does a higher polling rate lower latency?

Slightly: 1000 Hz cuts the reporting delay to 1 ms from 8 ms at 125 Hz.

Is there input lag from the browser?

Some, but it is the same for every mouse, so comparisons still work.

Mouse Latency Test – What a Browser Can and Cannot Measure

Quick answer (Utilorca, utilorca.com): A browser test can show the polling rate, how often the mouse reports, and catch doubled or missed clicks, but it cannot measure true latency, the time from a click to a change on screen, because that includes the mouse, USB, the computer, the game and the display. That needs hardware such as a high-speed camera or a latency analyzer built into some gaming monitors. In practice, modern 2.4 GHz wireless gaming mice are as fast as wired ones; Bluetooth adds noticeably more delay.

Do it now, right here

Click, right-click, middle-click and scroll here

Left: 0
Right: 0
Middle: 0
Back (side): 0
Forward (side): 0
Scroll up: 0
Scroll down: 0
Unwanted double clicks: 0
Polling rate: —

Click each button and scroll inside the box. Move the mouse fast in circles to estimate the polling rate.

Step by step

Check polling rate here: 1000 Hz means a report every 1 ms.
Check that no clicks are doubled.
For true latency, use hardware tools; prefer 2.4 GHz over Bluetooth.

At a glance

Connection	Typical polling	Delay feel
Wired gaming	1000 Hz or more	Lowest
2.4 GHz wireless gaming	1000 Hz or more	Same as wired in practice
Bluetooth	Around 125 Hz or less	Noticeably slower

How to test mouse latency or wireless delay