Letters stream by one at a time; you press only when the current letter matches the one shown N steps earlier. This is the exact task cognitive scientists use to measure working memory — and it gets serious at 2-back.

How to play

1. Pick a level on the title screen: 1-back through 5-back. Your choice is remembered in this browser for next time.
2. Press START. A reminder ("Tap when it matches n back!") shows for 3 seconds, then the first letter appears.
3. Letters change every 2 seconds: each one is shown large for 1.3 s, then only a dot (·) remains for 0.7 s. You can still press while the dot is showing.
4. If the current letter equals the letter N steps back, hit the big MATCH button or the space bar on a keyboard. Only one press per letter counts.
5. A correct press flashes the button and the letter green; a press on a non-match flashes the button pink.
6. When the letters-left counter reaches zero you get your accuracy plus a table of hits, misses and false alarms.

Rules and scoring

Letters	Eight: A · B · C · E · H · K · O · T
Stream length	24 scored letters plus N lead-in letters that have nothing to compare against. 2-back is 26 letters, roughly 52 seconds
Pace	One letter every 2 s: 1.3 s visible, 0.7 s blank
Match rate	About 30% of scored letters are matches; positions that would accidentally repeat are mostly swapped to a different letter
Accuracy	(24 − misses − false alarms) ÷ 24 × 100, rounded. Both caught matches (hits) and correctly ignored non-matches count as correct
Result message	92+ "working-memory monster", 80–91 "trained brain", 65–79 "above average", below that "N-back is all practice"
Leaderboard	2-back only for submissions and personal best. A higher n always outranks a lower one, then accuracy decides (score = n×1000 + accuracy); ties share the same rank. 1-back and 3-back results can be viewed and shared but not submitted

A repeated letter is only a match if it sits exactly N steps back. In 2-back, A · B · A is a match (the third letter equals the one two steps earlier), but A · A back to back is a 1-back repeat — pressing on it is a false alarm. Filtering out these lures is where scores are decided.

Why N-back is hard

1-back only asks you to remember the last letter. At 2-back you must take in each new letter, compare it against two ago, and shift your mental list one slot — all at once. That "maintain while updating" loop is the core of working memory, which is why N-back scores track focus and multitasking so closely.

In cognitive psychology N-back is the standard task for the updating function of working memory. Unlike a digit span test, it is not about how much you can hold but about swapping the contents continuously without losing the thread. That is also why brain-training apps lean on it — with the caveat that whether N-back practice improves anything beyond N-back itself is still debated among researchers.

Reading your score

Accuracy counts caught matches and correct passes. Many misses point to memory decay; many false alarms point to impulse control. Above 80% on 2-back is solid, 90%+ is trained. Everyone collapses at 3-back at first — no shame.

One trap to know: because only about 30% of letters are matches, never pressing at all yields roughly 70 points. So 70 is "the same as not playing", and real skill shows from 80 upward. Pressing on every letter goes the other way, piling up false alarms and landing near 30.

Tips

• Sub-vocalize in rhythm. Turning the stream into inner speech ("A, B, A…") makes the letter from N steps back easier to retrieve.
• Use the 0.7-second dot. Your response counts until the next letter appears, so pressing once you are sure is not too late.
• Learn the pace on 1-back, then move to 2-back. Once the 2-second rhythm feels natural, 2-back scores jump.
• Use the space bar. On a keyboard you can keep your eyes on the letter instead of the button.

Frequently asked questions

Why are 1-back and 3-back scores not ranked?

Scores from different difficulties cannot be lined up in one list. The leaderboard and your personal best count only the standard 2-back; other levels show the result and can be shared.

What if I press twice on one letter?

Only the first press counts; the second is ignored, so you do not collect two false alarms.

What does an accuracy of 0 mean?

It happens only when false alarms are extreme, such as pressing on every letter. In that case the submit form does not open.

How do I compare with a friend?

The share link carries both your accuracy and the level. When a friend opens it, the title screen shows "A friend scored n".

Related tools

Try sequence memory, number memory or the Stroop test — all free.

• Sequence Memory Test — visuospatial working memory measured as pure capacity, with no updating.
• Digit Span Memory Test — how many digits your verbal working memory can hold.
• Stroop Test — if you had many false alarms, measure inhibitory control on its own.
• Reaction Time Test — if the 2-second pace felt slow, check your raw reaction speed.