Reaction Time Test

Reaction time is the interval between the onset of a stimulus and the beginning of a voluntary motor response. It is divided into two phases: pre-motor time (neural signal processing) and motor time (muscle activation). The sum of both is measured in milliseconds (ms).

Simple reaction time formula: RT = Stimulus Detection Time + Neural Processing Time + Motor Execution Time

In practice, RT is measured directly as: RT = Response Time (ms) − Stimulus Onset Time (ms)

Hick’s Law: choice reaction time: When a person must choose between n equally likely options: RT = a + b × log₂(n + 1)

Where:

• a = base reaction time (constant, ~150 ms)
• b = time per bit of information processed (~150 ms/bit)
• n = number of choices

The + 1 is not decoration and it is the part most summaries drop. Hyman added it in 1953 to account for the uncertainty of whether to respond at all, not just which response to make. Without it, one choice comes out at the base time with no decision cost, which is wrong: even a single-option task has a go/no-go decision in it.

Example: 1 choice → log₂(2) = 1 → RT ≈ 150 + 150 = 300 ms. 4 choices → log₂(5) = 2.32 → RT ≈ 150 + (150 × 2.32) = 498 ms.

Hold that 300 ms against the age table below, which puts simple RT for a healthy adult at 190 to 220 ms, and the formula looks broken. It is not, but the reason is worth spelling out because almost nobody does. The formula is not predicting simple RT at n = 1, it is predicting go/no-go RT. Simple RT is measured with the response certain: the light comes on, you press. Go/no-go adds the question of whether this signal is the one you act on, and that question costs about 100 ms whether or not you end up moving. Both numbers are correct measurements of different tasks. The table below is simple RT; do not compare it to a formula that has a decision baked in.

The Hick’s law calculator runs this properly and lets you set a and b yourself, since both vary a lot by response type.

Average reaction times by age (visual stimulus, simple RT, lab apparatus):

(Elite figures are only listed where competitive-athlete data exists for that band. Nobody has published a meaningful elite average for a 12-year-old or a 70-year-old.)

Why the test above rates you slower than that table

Those numbers come from purpose-built lab equipment, where a photodiode watches the lamp and a microswitch catches the finger. A test running in a web browser has to wait for the screen to actually refresh, for the operating system to notice the click, and for JavaScript to get a timestamp. That stack adds roughly 50 to 100 ms that has nothing to do with your nervous system, which is why online tests cluster around 250–280 ms while the lab tables say 200–230 ms for the same people.

So use the rating on this page to compare yourself against other people taking browser tests, and use the table to understand where simple reaction time actually sits. Do not read a 260 ms browser result as “worse than a 55-year-old”. It is not measuring the same thing. A 60 Hz monitor alone contributes up to 16.7 ms of pure display lag; a 144 Hz gaming panel cuts that to 7 ms, which is a real and slightly unfair advantage in any online test.

Factors that slow reaction time:

• Alcohol (+15–30% slower per drink)
• Sleep deprivation. Two weeks of 6-hour nights degrades response speed about as much as going two full nights without sleep at all (Van Dongen et al., 2003), and the people in that study rated themselves as only slightly sleepy throughout.
• Distraction (texting while driving adds ~570 ms on average)
• Age (peaks at ~24, declines ~3 ms/year after 40)

Worked example: A driver traveling at 100 km/h (27.8 m/s) with a 250 ms reaction time: Distance covered during reaction = 27.8 × 0.250 = 6.9 meters before brakes are even applied.

Improving reaction time: regular exercise, adequate sleep, caffeine (up to ~200 mg), and sport-specific drills all measurably reduce RT by 5–20%.