How BedsideLingo decides when a phrase comes back

What spaced repetition is

Memory fades over time, and it fades fastest right after you learn something. Reviewing a phrase just before you would forget it strengthens the memory far more than reviewing it too early or too late.

Spaced repetition turns that into a schedule. Each time you recall a phrase, the next review is pushed further away. Each time you forget it, the gap shrinks again. Over time you spend your practice on the phrases that need it, instead of on the ones you already know.

How FSRS works

FSRS stands for Free Spaced Repetition Scheduler. It models each phrase you practise using three ideas about memory:

• Difficulty: how hard this phrase is for you to remember.
• Stability: how strongly the phrase is stored in your memory. The higher it is, the more slowly you forget it.
• Retrievability: how likely you are to recall the phrase right now. It is highest just after a review and drops as time passes.

After every answer, FSRS updates its estimate for that phrase. A correct answer raises stability, so the next gap is longer. A wrong answer lowers it, so the phrase returns sooner. The scheduler then sets the next review for roughly the moment your chance of remembering falls to a target level. The library BedsideLingo uses aims for about 90 percent by default.

FSRS builds on earlier research. Its authors describe it as springing from MaiMemo’s DHP model, which is a variant of the DSR model (difficulty, stability, retrievability) proposed by Piotr Wozniak.

How BedsideLingo uses it

1. You practise and answer. Each phrase shows up, you try to recall it, and you say how it went.
2. Your answer sets the next date. The app passes your answer to FSRS, which returns the next due date. Reviews that are due come first in a practice session.
3. Progress is kept per phrase and per language. Learning French and learning Spanish keep separate schedules, and so do the two directions of a phrase.
4. “I’ve learned it” is your call. If you are sure of a phrase, you can mark it learned. The app then checks back after a few months, a gap you can change in Settings.
5. Bedside playback is separate. Playing a phrase at the bedside never counts as a review and never changes your schedule.
6. Everything stays on your device. The scheduling runs locally, with no account and no upload.

One limit: BedsideLingo uses FSRS with its default settings and with randomised spacing turned off, so the schedule is predictable. It does not yet tune the settings to your own review history.

Open source and credits

The source code of FSRS and its libraries is public, and anyone may use, study and modify it under the license terms.

• FSRS is developed by the Open Spaced Repetition community. The project describes itself as an independent open-source project driven by its community, and as springing from MaiMemo’s DHP model.
• ts-fsrs is the TypeScript implementation of FSRS that BedsideLingo uses (version 5.4.2), published by the same community at github.com/open-spaced-repetition/ts-fsrs. The package lists ishiko as its author. According to its documentation, this version implements FSRS-6.
• The algorithm’s home is free-spaced-repetition-scheduler, where the model and its documentation are kept.

We are grateful to everyone who built and maintains these projects. BedsideLingo is not affiliated with or endorsed by them.

ts-fsrs license

ts-fsrs is released under the MIT License:

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