FSRS is the most significant improvement to Anki in years. Here's what it is, why it's better than SM-2, how to enable it, and what to set your retention target to.
FSRS (Free Spaced Repetition Scheduler) is a new scheduling algorithm built into Anki that replaces the old SM-2 algorithm. It's based on a modern memory model, learns from your individual review history, and requires fewer reviews to achieve the same retention rate - typically 15–20% fewer reviews.
FSRS is based on the DSR (Difficulty, Stability, Retrievability) model of memory. Three variables govern every card:
How intrinsically hard is this card? Some cards are just harder to remember than others - different content, different connections, different personal relevance. FSRS tracks this per-card rather than applying a one-size-fits-all ease factor.
How long until you forget this card? Stability increases each time you successfully recall it. A card you've reviewed 10 times has much higher stability than one you've reviewed twice. FSRS uses this to schedule reviews at the optimal moment.
What is the probability you can recall this card right now? This decays over time following a forgetting curve. FSRS shows you the card when R drops to your target retention level (e.g., 90%). That's the optimal review moment - not too early (wasting a review), not too late (after forgetting).
Requires Anki 23.10 or later. Update Anki first if needed.
| Retention | Reviews per day | Best for |
|---|---|---|
| 0.70 | Very low | Language learning, low-stakes content |
| 0.80 | Low | General studying, moderate importance |
| 0.90 | Moderate (recommended default) | Most learners - good balance |
| 0.95 | High | Medical school boards, high-stakes exams |
| 0.97+ | Very high | Not recommended - exponentially more reviews for marginal gain |
Note: Going from 90% to 95% retention roughly doubles your daily review count. Going to 97% quadruples it. The marginal benefit of each additional percentage point decreases while the cost increases sharply. 90% is the sweet spot for most learners.
The FSRS4Anki Helper add-on (code: 759844606) adds a full control panel for FSRS management. It lets you:
Related: Anki settings complete guide, spaced repetition schedule explained, what is spaced repetition.
Unlike the old SM-2 algorithm, which used static formulas, FSRS is a machine learning model. When you click "Optimize," Anki analyzes your actual review history—every "Again," "Hard," "Good," and "Easy" you've ever pressed—to calculate the specific weights that describe your unique memory patterns. This means the algorithm adapts to how you personally forget information, rather than relying on a generic average of all users.
To get the most out of this personalization, keep these optimization tips in mind:
One of the most powerful features of FSRS is the ability to choose your "Desired Retention." However, many new users make the mistake of setting this too high. In spaced repetition, there is a non-linear relationship between the percentage of memory retained and the amount of time spent reviewing. This is known as the efficiency frontier.
As you push your retention target higher, the workload increases exponentially. For example, moving from 85% to 90% retention might add a manageable number of reviews to your day. However, moving from 95% to 97% can nearly double your workload for a marginal 2% gain in memory. This is often a poor trade-off in terms of time management.
It is important to remember that FSRS is a scheduling tool, not a learning tool. While it optimizes when you see a card, it cannot fix a poorly written card. If a card is too wordy, ambiguous, or contains too many ideas, you will find yourself hitting "Again" regardless of how advanced the algorithm is. This creates "leech" cards that waste your time and skew your FSRS data.
To truly unlock the power of FSRS, you must pair it with the principle of atomicity—breaking information down into its smallest possible components. This ensures that the "Difficulty" variable in the DSR model remains stable and predictable.
Now that your FSRS settings are optimized, fill your deck. StudyCards AI generates properly structured flashcards from your notes and exports them directly to Anki - ready for FSRS scheduling from card one.
Start Free - Build Your FSRS Deck →Generate Anki flashcards free