Tune FSRS retention

Adjust how aggressively FSRS schedules your Items, and keep its parameters fit to your own history.

Before you begin

• These controls live in Settings, in the Item scheduler section. They apply to Items (flashcards) only. Topics and Extracts use the separate Topic scheduler below them.
• Settings, FSRS parameters, and run history are stored per Collection. Switch to the Collection you want to tune first.
• For the theory behind retention, stability, and difficulty, see Spaced repetition.

Caution

Changing retention or parameters affects future scheduling only. It does not rewrite the due dates of Items you have already reviewed. To move existing due dates, use Reschedule existing Items.

Set your retention target

Retention is the probability of recall you aim for at the moment an Item is due. Higher retention schedules each Item sooner and means more reviews; lower retention means fewer reviews but more lapses.

1. Open Settings and find the Item scheduler section.
2. Drag the Desired retention slider. It ranges from 70% to 99% in 1% steps; the default is 90%. The recommended range is 85–95%.
3. Select Save settings (or Save in the unsaved-changes banner) to persist the change.

Note

The slider only updates the form until you save. While Desired retention has unsaved changes, Run optimization and Roll back are disabled, with the hint “Save retention changes before running optimization or rolling back.”

Optimize parameters from your history

Optimization tunes Kioku’s FSRS scheduling to your own review history, and keeps the result only when it predicts your recall better than your current parameters.

1. Save any pending retention change first (see above).
2. Under Parameter optimization, select Run optimization. The button reads Optimizing… while the run is in progress.
3. Read the outcome banner:
   • FSRS parameters optimized and activated — the new parameters predicted your recall better and are now active.
   • FSRS optimization completed but the candidate was rejected — your current parameters held up, so nothing changed. This is normal, not an error.
   • A failure banner reports the reason the run did not complete.

Note

Optimization needs at least 100 reviews in the Collection. The availability text shows your count, for example “160 reviews available. Minimum 100.” Below the minimum, Run optimization stays disabled.

Optimization may also adjust your saved Desired retention slider to a value that fits your history better, so it can move after a run even though you did not touch it.

Roll back to an earlier run

Expand Run history to list recent runs; the active parameters are tagged Active. Each accepted, non-active run has a Roll back button. Selecting it opens a Rollback FSRS params confirmation; confirm to restore that run’s parameters. Roll back is disabled while you have unsaved retention changes.

Reschedule existing Items

Tuning FSRS never moves the due dates of Items you have already reviewed. Rescheduling is a separate, per-Element action.

1. In Browse, select an Item and run the Reschedule… operation (keyboard shortcut P). In Review, press P while the Item is showing.
2. In the Reschedule dialog, pick a quick option — Tomorrow, +3 days, +1 week, or +1 month — or choose a date under Or pick a date.
3. Select Save. A Rescheduled confirmation appears and the new due date takes effect.

Caution

Relative quick picks shift from the Item’s existing due date when that date is in the future, not always from today — so +1 week can mean seven days past an already-future due date.

This changes one Element at a time. There is no bulk “reschedule everything” tied to FSRS tuning; to shift a whole Topic branch forward, use the Postpone Branch action.

Result

Your Collection now schedules Items at your chosen retention, optionally using parameters fit to your own history. Existing due dates stay put until you reschedule them individually.

Related

• Spaced repetition
• Glossary: Retention
• Glossary: FSRS