Spaced repetition shows each flashcard at a growing interval timed to just before you would forget it, which is the most efficient way to commit facts to long-term memory. This calculator runs the exact SM-2 algorithm that powers Anki so you can see how a single review reschedules a card.
How it works
SM-2 tracks three values per card: the repetition count n, the ease factor EF,
and the interval I in days. After grading your recall quality q from 0 to 5,
the new ease factor is:
EF' = EF + (0.1 - (5 - q) * (0.08 + (5 - q) * 0.02))
EF' = max(EF', 1.3)The next interval is then chosen by repetition number:
if q < 3: n = 0, I = 1 (failed — restart)
if n == 1: I = 1
if n == 2: I = 6
if n >= 3: I = round(previous I * EF')Example and tips
A card on its third repetition with ease factor 2.5 and a previous interval of 6 days, answered with quality 4, keeps an ease factor near 2.5 and schedules the next review at about 15 days out (6 × 2.5). Be honest with your recall grade: rating cards too generously inflates intervals and you forget; rating too harshly buries you in needless reviews. Quality 3 means you recalled it but with serious effort.