If you've ever taken a reaction time test on a laptop trackpad and then again on a wired gaming mouse, you've felt the difference. The mouse feels snappier. The score is lower. The test suddenly seems easier. What you're experiencing is input lag — the delay between your physical action and the moment the computer registers it. And it's almost certainly bigger than you think.
This post breaks down where input lag comes from, how much it's actually costing you, and how to minimise it without spending a fortune.
Where the latency comes from
Every step between your finger moving and the test registering a click adds a few milliseconds. Most of these are invisible, but they add up. Here's the full chain, roughly in order of impact:
- Mouse polling rate — a 125 Hz mouse (typical office wireless) checks for clicks every 8 ms. A 500 Hz mouse checks every 2 ms. A 1000 Hz gaming mouse checks every 1 ms.
- Bluetooth latency — Bluetooth adds 8–15 ms of latency for pairing, encryption, and retransmission. A 2.4 GHz wireless dongle avoids this. A wired connection avoids it entirely.
- Trackpad debounce — laptop trackpads have aggressive debounce algorithms to filter out accidental touches. This adds 30–50 ms of latency. Trackpads are the worst input device for RT testing.
- Monitor refresh — a 60 Hz monitor updates every 16.67 ms. The colour change might not be visible until the next refresh cycle, costing up to 16 ms. A 144 Hz monitor costs up to 7 ms. A 240 Hz monitor costs up to 4 ms.
- Pixel response time — even after a monitor refreshes, the pixels take time to actually change colour. Cheap IPS panels: 5–10 ms. TN panels: 1 ms. OLED: <0.5 ms.
- Operating system scheduling — your OS doesn't process input instantly; it queues events and processes them on the next scheduler tick. Usually 1–3 ms on modern OSes, but can spike under load.
- Browser overhead — JavaScript event handling adds 1–5 ms. Modern browsers using the performance API (which this site uses) keep this close to 1 ms.
Add all of these up for a typical office setup — Bluetooth mouse, 60 Hz monitor, trackpad as fallback — and you can easily be carrying 60+ ms of latency that has nothing to do with your nervous system. That's the difference between a 250 ms score and a 310 ms score, with zero biological change.
How to minimise it
The good news is that most of the wins here are cheap. You don't need a $200 mouse or a $1000 monitor — you need to avoid the worst offenders.
First, switch from a trackpad to any mouse. Even a cheap office mouse is better than a trackpad. The debounce algorithms on trackpads are the single biggest source of avoidable latency in most setups.
Second, prefer wired over wireless. A $15 wired Logitech mouse will outperform a $100 Bluetooth mouse for RT testing, because Bluetooth adds 8–15 ms of latency that wired connections simply don't have. If you must go wireless, use a 2.4 GHz dongle, not Bluetooth.
Third, if you have a high-refresh-rate monitor, use it. A 144 Hz monitor costs $150 and saves 7–10 ms over a 60 Hz panel. A 240 Hz monitor costs $300 and saves another 3 ms. The jump from 60 to 144 is the most cost-effective upgrade; beyond that, diminishing returns kick in.
Fourth, turn off mouse acceleration in your OS. Mouse acceleration changes the relationship between physical movement and cursor movement based on speed, which makes your aim inconsistent. It doesn't directly add latency, but it makes your clicks less precise, which costs you time.
What about gaming peripherals?
High-end gaming mice ($80–$150) typically have 1000 Hz polling, optical switches (which avoid debounce), and weigh under 70 grams. These are genuinely better than cheap office mice, but the advantage over a basic wired mouse is small — maybe 2–5 ms total. Worth it if you're a competitive gamer, not worth it if you just want an honest RT score.
Mechanical keyboards are similar. They feel better and last longer, but the latency advantage over a decent membrane keyboard is 1–3 ms. Most casual users won't notice. If you're testing RT with the spacebar, use whatever keyboard you have — the difference is negligible.
How to tell if input lag is hurting you
The simplest test: take the reaction time test on your current setup, then take it again on a friend's setup with a wired mouse and a 144 Hz monitor. If your score drops by 20+ ms on the better setup, input lag was a significant factor.
If you can't do that side-by-side test, here are warning signs: your score is above 320 ms despite feeling like you reacted quickly; your score varies dramatically between devices; you can 'feel' the delay between clicking and the click registering. Any of these suggest input lag is contributing to your score.
The honest baseline for a modern setup with a wired mouse and a 60 Hz monitor is about 250 ms for an adult in their 20s. If you're posting 280+ ms on that setup and you're well-rested, either you're outside the typical range (which is fine) or something else is adding latency. A $25 wired mouse is the cheapest way to find out.