How to Enable FSRS in Anki

What Is FSRS and Why Is It Better Than SM-2?

SM-2, the algorithm Anki has used since the 1980s, treats every learner's memory the same way. It assigns intervals based on a fixed ease factor and doesn't account for how your personal forgetting curve actually behaves. FSRS, developed by Jarrett Ye and published in 2022, was trained on over 700 million real flashcard reviews. It models three variables per card — Difficulty (D), Stability (S), and Retrievability (R) — and schedules each review precisely when your probability of recall drops to your target retention level (typically 90%). Because it learns from your actual review history, FSRS personalizes intervals in a way SM-2 simply cannot. Multiple independent studies confirm FSRS achieves equivalent long-term retention while requiring 20–30% fewer reviews. For someone doing 200 reviews a day, that's 40–60 reviews saved daily — hundreds of hours per year.

FSRS 4.5 vs Older Versions — What Changed?

Anki currently ships with FSRS-4.5, a significant refinement over the original FSRS v4. The key improvements in 4.5 include a more accurate stability-after-forgetting model, better handling of short-interval reviews (reviews done earlier than scheduled), and improved initial stability estimates for new cards. Earlier versions (FSRS v3, v4) used a simpler forgetting equation that underestimated how quickly difficult cards decay. FSRS-4.5 corrects this with a revised loss function trained on a larger, more diverse dataset. If you installed FSRS via an Anki add-on before 2024, you were likely on v4 or v3. Anki 23.10 and later bundles FSRS-4.5 natively — no add-on required. It's strongly recommended to migrate: go to Tools → Preferences → Review and enable the native FSRS rather than using legacy add-ons.

Step-by-Step: How to Enable FSRS in Anki

Enabling FSRS in Anki takes under two minutes. Make sure you're running Anki 23.10 or later (check Help → About). The process is the same on Windows, macOS, and Linux.

• Open Anki and click Tools in the top menu bar
• Select Preferences from the dropdown
• Click the Review tab at the top of the Preferences window
• Check the box labeled "Enable FSRS"
• Set your desired Desired Retention — 0.90 (90%) is recommended for most learners
• Click OK to save — FSRS is now active for all new reviews
• Optionally, reschedule existing cards: click "Reschedule cards on change" before saving to apply FSRS intervals to your entire collection immediately

How to Optimize FSRS Parameters for Your Deck

The default FSRS parameters work well, but the real power of FSRS comes from personalizing those parameters to match your memory. Anki's built-in optimizer analyzes your review history and fits a custom set of 17 parameters specifically to how your brain retains information. More review data = more accurate personalization. Aim for at least 1,000 reviews before optimizing, and ideally 3,000+.

• Go to Tools → Preferences → Review and ensure FSRS is enabled
• Click "Optimize FSRS Parameters" — Anki will analyze your full review history
• Wait for the optimization to complete (can take 1–5 minutes for large collections)
• Review the new parameter values — the optimizer will show a loss score; lower is better
• Click "Apply" to save the optimized parameters
• Re-run the optimizer every few months as your review history grows
• For multiple decks with very different content (e.g., language vocab vs. medical anatomy), consider setting deck-specific parameters via the deck options

Common Mistakes When Setting Up FSRS in Anki

Many users enable FSRS but then undermine it through configuration errors or habit carry-overs from SM-2. These are the most frequently reported mistakes and how to avoid them.

• Setting retention too high: Pushing desired retention above 95% dramatically increases review load. 90% is the scientifically validated sweet spot balancing memory strength and workload.
• Running the optimizer too early: With fewer than 500 reviews, the optimizer has too little data and may produce worse parameters than the defaults. Wait until 1,000+ reviews.
• Leaving legacy SM-2 add-ons active: Old FSRS or scheduling add-ons can conflict with native FSRS. Disable all scheduling add-ons before enabling native FSRS.
• Manually burying or rescheduling cards: FSRS needs consistent review data to learn your patterns. Frequent manual rescheduling pollutes its model.
• Not rescheduling existing cards: Cards reviewed under SM-2 carry SM-2-era intervals. Check "Reschedule cards on change" to let FSRS recalculate intervals for your whole collection.
• Confusing 'Hard' with 'Again': In FSRS, pressing Hard still moves the interval forward. Press Again only when you genuinely couldn't recall the answer.

SM-2 vs FSRS — Side-by-Side Comparison

Choosing between SM-2 and FSRS isn't really a close call for most users. Here's how they compare across the metrics that matter for daily studying.

Want FSRS Without Any Setup? Try Flica

Anki's FSRS integration is excellent, but it was added years after launch — which means enabling it requires navigating menus, understanding parameters, running the optimizer, and avoiding a handful of configuration traps. Flica is a flashcard app built around FSRS from the very first line of code. When you open Flica for the first time, FSRS is already running. There are no preference menus to navigate, no optimizer to manually trigger, and no risk of conflicting add-ons. Flica also includes AI-powered card generation: paste a YouTube URL or a PDF, and the AI creates optimized flashcards automatically. You focus entirely on reviewing — the algorithm handles everything else. Flica is available for free on iOS and Android.