Revising everything, all the time, does not hold up over the length of a preparation. Spaced repetition solves the problem differently: each question is put back in front of you just before the moment you are likely to forget it. No earlier, which would waste your time on what you already know, and no later, which would make you relearn everything.
This page describes exactly the algorithm in place, the figures it uses and what it cannot do yet.
We use FSRS, a free and maintained spaced repetition scheduler, adopted by Anki since 2023. Our implementation is the official TypeScript port of the algorithm, with its twenty-one parameters, and not an in-house approximation.
FSRS does not keep a score, but two quantities for each candidate and question pair. Difficulty, on a scale of 1 to 10, says how much this question costs you, personally. Stability, expressed in days, says how long your memory holds before falling back to the target recall level, set at 90 per cent.
The time elapsed since you last met the question is part of the calculation. Answering correctly the next day and answering correctly six months later do not say the same thing about your memory, and therefore do not produce the same next interval.
Most spaced repetition tools ask the user to rate themselves after the fact: easy, medium, hard. In competition training, that extra question breaks the rhythm and rests on a judgement that is unreliable just after seeing the correct answer. We infer the rating from what you actually did.
Speed is measured as a share of the time allowed for the question, not in absolute seconds: our durations run from 30 to 150 seconds depending on the question, and the same duration does not mean the same thing on numerical reasoning and on a knowledge question.
On a run of correct answers at the normal pace, a new question comes back after 3 days, then 14, then 57, then 196. Beyond that, the interval is capped at one year: a competition preparation plays out over months, and a question scheduled beyond the date of the test is of no use to anyone.
A wrong answer brings the due date back to the next day and lowers stability, without erasing what you had built: the difficulty the question has acquired is kept, and the climb back is simply slower than a first learning.
A question becomes acquired after three consecutive correct answers at the normal pace, which corresponds to a next due date about two months away. Three laboured correct answers are not enough: the stability reached stays below the threshold, and the question stays in revision.
The speed thresholds are provisional. They were set on the actual distribution of our users' correct answers, but on a sample that is still small. They will be recalibrated when the volume allows it, and this page will be updated on the day they change.
The parameters of the algorithm are the FSRS default parameters, the same for everyone. FSRS can optimise itself on each user's personal history; we do not do that yet, for want of a history large enough for the optimisation to be better than the default rather than worse.
Finally, no manual adjustment is offered: you can neither force a question to come back earlier, nor take it out of the queue. It is a choice of simplicity that we will look at again if you tell us that it is missing.
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