FSRS (Free Spaced Repetition Scheduler) v6 is the most advanced open-source scheduling algorithm for flashcards. It powers both Anki (via plugin) and Forgetless (built-in). This guide explains how it works, how to get the best results, and why it outperforms older methods like SM-2.
FSRS is a spaced repetition algorithm based on the DSR (Difficulty, Stability, Retrievability) model of memory. Unlike older algorithms that use fixed intervals, FSRS models your actual forgetting curve and adapts to your individual memory patterns.
It was created by Jarrett Ye and has been adopted by the Anki community as the successor to SM-2. Research shows FSRS reduces the number of reviews needed by up to 30% while maintaining the same or better retention rates.
After seeing the answer, you rate how well you remembered: Again, Hard, Good, or Easy. This rating feeds into the algorithm.
Difficulty (how hard the card is for you), Stability (how long until you forget), and Retrievability (the probability you can recall it right now). These are unique per card.
Based on your target retention rate (default 90%), FSRS calculates exactly when to show the card again — right before you would forget it. No wasted reviews.
| Forgetless | Anki | |
|---|---|---|
| FSRS version | v6 (built-in) | v6 (requires plugin) |
| Setup | Works out of the box | Install add-on, enable in settings |
| Target retention | Adjustable (default 90%) | Adjustable (default 90%) |
| Parameter optimization | Automatic | Manual (Tools → Optimize) |
| Cross-device sync | Automatic | Requires AnkiWeb sync first |
| AI card generation | Built-in | Not available |
FSRS works well with default settings, but here are tips to get even better results:
The default is 90%, which means you'll remember approximately 9 out of 10 cards at review time. If you're preparing for a high-stakes exam, increase it to 92-95%. For casual learning, 85-88% reduces review load significantly. Higher retention means more frequent reviews — find your balance.
FSRS learns from your ratings. If you rate cards as "Good" when you actually struggled, the algorithm will space them too far apart and you'll forget. Be honest: use "Again" when you didn't remember, "Hard" when it took effort, "Good" when you recalled it, and "Easy" only when it was effortless.
FSRS schedules your reviews at specific times for a reason. Skipping days lets cards pile up and reduces the algorithm's effectiveness. A few minutes every day is far better than an hour once a week. Use streak tracking to build the habit.
FSRS was originally developed for the Anki community, where it's used by medical students, law students, and language learners worldwide. Forgetless makes it accessible to everyone — no plugin installation, no configuration. Sign up and the algorithm starts working for you immediately.
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