How SM-2 Spaced Repetition Works — and Why It Beats Cramming

Spaced repetition with the SM-2 algorithm schedules each flashcard review for the moment just before you would forget it, stretching the gap a little wider every time you recall the word correctly. That timing is what makes it far more efficient than cramming: you spend review time only on the words at risk of slipping away, not the ones you already know.

The problem SM-2 solves: the forgetting curve

In the 1880s, Hermann Ebbinghaus showed that memory decays exponentially. Learn a list of words today and, without review, you'll have forgotten most of them within a week. Each time you successfully recall something, though, the curve flattens — the memory lasts longer before it fades again.

Cramming ignores this. Reviewing fifty words ten times in one evening produces ten reviews crammed into the steepest part of the curve, where the memory is still fresh and the review adds almost nothing. The next morning the words are gone anyway.

How the SM-2 algorithm schedules reviews

SM-2, designed by Piotr Woźniak in 1987 for SuperMemo, assigns every card three pieces of state:

• Interval — how many days until the next review.
• Repetitions — how many times in a row you've recalled it correctly.
• Ease factor — a multiplier (starting at 2.5) that controls how fast the interval grows.

After each review you grade your recall. On a correct answer the interval grows: the first success schedules the card one day out, the second six days, and from then on the previous interval is multiplied by the ease factor. A card you keep getting right quickly jumps to intervals of weeks, then months — you simply stop seeing it often, because you don't need to.

When you fail a card, SM-2 resets the interval to the beginning and lowers the ease factor slightly, so a word you find genuinely hard comes back sooner and more often than an easy one. Over time the algorithm tunes itself to your memory of each specific word.

Why this beats cramming for IELTS

IELTS rewards a wide, active vocabulary — the kind you can produce under exam pressure, not just recognise. Two properties of spaced repetition map directly onto that:

1. Active recall. Each review forces you to retrieve the word before flipping the card. Retrieval practice builds far stronger memories than re-reading a list.
2. Efficient coverage. Because easy words drift to long intervals, your daily review stays small even as your deck grows into the hundreds. You can maintain 500+ academic words in a few minutes a day — impossible by cramming.

The result is durable: words you reviewed weeks ago are still available on exam day, because the algorithm kept resurfacing them at exactly the right moments.

How voxara uses SM-2

voxara implements the classic SM-2 schedule for every flashcard. New words you add — or import from a public IELTS deck — enter the queue, and the daily review surfaces only what's due. You grade each card, the interval and ease factor update, and the next review date is set automatically. Nothing to plan; the algorithm decides what you see and when.