SM-2 Algorithm Explained: Spaced Repetition Basics
A plain-English guide to the scheduler behind many flashcard habits
TL;DR
SM-2 schedules reviews by using your recall grade to decide the next interval. It is simpler than FSRS, but still useful when cards are clean and review habits are consistent. If card creation is the bottleneck, Flica can help you make smaller, clearer decks before the scheduler matters.
You can lose hours tuning Anki settings before you know what the scheduler is doing. That is backwards: the algorithm is only useful when the card is clear and the review habit survives the week.
This guide explains SM-2 without pretending that one setting fixes every study problem. You will see when SM-2 is enough, when FSRS is worth considering, and how to make a deck that either scheduler can handle.
What SM-2 actually does
SM-2 is the older spaced repetition scheduling idea that made digital flashcards practical. After each review, the learner grades recall quality. The scheduler then lengthens or shortens the next interval. A good answer pushes the card further into the future, while a weak answer pulls it back. That simple feedback loop is why many learners first meet spaced repetition through Anki.
Why the algorithm still matters in 2026
Even with newer schedulers around, SM-2 still matters for a practical reason: before you trust an app with months of study time, you want to know how it decides when you see a card again. SM-2 is easy to understand, easy to explain, and good enough for many steady review habits. Its weakness is that it treats the learner and the card with a broad rule rather than a more personalized memory model.
SM-2 vs FSRS at a glance
Use this comparison before changing settings. The goal is not to pick the most technical option. The goal is to keep reviews predictable enough that you actually finish them. For a full head-to-head with real scheduling examples, see our FSRS vs SM-2 comparison.
| Question | SM-2 | FSRS |
|---|---|---|
| Core idea | Interval grows from recall grades | Model estimates memory state |
| Setup | Simple and familiar | Needs supported settings |
| Best for | Stable basic decks | Large or uneven decks |
| Risk | Intervals can feel rough | Settings can confuse beginners |
When SM-2 is enough
SM-2 is enough when your deck is small, the material is familiar, and you can review every day. Language vocabulary, simple definitions, and exam facts often work fine when cards are clear. If your problem is that cards are messy or you keep skipping reviews, changing algorithms will not fix the root cause.
When to consider FSRS or Flica
Consider FSRS when reviews feel badly timed, when you have many mature cards, or when the cost of forgetting is high. Our FSRS algorithm guide explains how it models your memory. Flica keeps the workflow lighter by combining AI card creation with spaced repetition so the bottleneck is not setup. That matters for learners who spend more time formatting decks than reviewing them.
A practical setup checklist
Before judging any algorithm, clean the deck first.
- One fact or decision per card.
- No huge paragraph answers.
- Review daily for at least two weeks.
- Suspend cards you repeatedly fail because of wording.
- Change one setting at a time.
FAQ
Is SM-2 the same as Anki?
No. Anki has used SM-2 style scheduling historically, but modern Anki also supports FSRS. SM-2 is the scheduling idea, not the whole app.
Is FSRS always better than SM-2?
Not always for every learner. FSRS can be more adaptive, but clear cards and consistent reviews matter more than algorithm labels.
Should beginners change settings first?
Usually no. Beginners should make a small clean deck, review daily, and only adjust settings after they see a real problem.
How does Flica fit this?
Flica is useful when creating clean cards is the bottleneck. It helps draft cards and keeps review simple so the schedule has better material to work with.
Use the algorithm, but fix the workflow first
SM-2 is not magic. It is a simple feedback loop that rewards remembered cards with longer intervals and brings forgotten cards back sooner.
If you want less setup, start with a small Flica deck, review it consistently, and only then decide whether advanced scheduling is worth your attention.
Make cleaner cards before tuning settings
Use Flica to turn notes into a small reviewable deck, then let spaced repetition do its job.
Related Articles
References
- SuperMemo documentation: the SM-2 algorithm.
- Anki manual: spaced repetition and FSRS documentation.