What is FSRS?
Updated 2026-06-20
FSRS — the Free Spaced Repetition Scheduler — is a modern algorithm that predicts, for each card, the moment your memory of it is about to fade, and schedules your next review right then. It's the scheduler behind Recense, and the one Anki adopted to replace its decades-old SM-2.
The problem it solves
Review a card too soon and you waste time on something you still know. Review it too late and you've already forgotten — back to square one. The sweet spot is the moment just before you'd forget. FSRS estimates that moment for every card and every person.
How it works
- It models memory with three values per card: retrievability (how likely you are to recall it now), stability (how slowly it fades) and difficulty.
- After each review, your rating updates those values — a card you found easy gets a longer gap; one you struggled with comes back sooner.
- It schedules the next review to hit a target recall probability (for example, 90%), so you study at the efficient edge of remembering.
FSRS vs SM-2
Older schedulers like SM-2 multiply intervals by a fixed factor regardless of how memory actually behaves. FSRS was fit to millions of real reviews, so it adapts to you and to each card — typically the same retention for noticeably fewer reviews.
What it means in practice
You don't tune anything. You rate how a card went, and FSRS handles the timing — fewer wasted reviews, better long-term retention, and a daily queue that reflects what you're actually about to forget.
Frequently asked
- What does FSRS stand for?
- Free Spaced Repetition Scheduler — an open algorithm that schedules flashcard reviews based on a model of human memory.
- Is FSRS better than SM-2?
- For most learners, yes: because FSRS was trained on large amounts of real review data, it usually achieves the same retention with fewer reviews than the older SM-2 algorithm.
- Do I need to configure FSRS in Recense?
- No. FSRS is on by default. You just rate each card and the scheduler does the rest.
Study on an FSRS schedule
Let the algorithm pick the moment. You just review.
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