The evolution of spaced repetition algorithms
Spaced repetition is based on a well-documented psychological principle: the human brain forgets new information along a predictable mathematical decay curve. If you review a concept right before you are about to forget it, the memory trace becomes significantly stronger, and the forgetting curve flattens out.
For more than thirty years, study software relied almost exclusively on the SuperMemo SM-2 algorithm, developed in the late 1980s. While SM-2 was groundbreaking for its time, it uses rigid heuristics that often cause ease hell: penalizing cards too harshly when you miss them once, and forcing students into endless daily backlogs of hundreds of repetitive reviews.
FluxNote uses the modern Free Spaced Repetition Scheduler (FSRS) algorithm, an open-source, machine-learning-informed model that predicts human memory retention with significantly higher accuracy.
How FSRS models human memory
FSRS evaluates three distinct parameters for every single flashcard in your deck:
How Long Memory Lasts
The number of days it takes for your probability of recalling the card to fall from 100% down to 90%. As stability increases, intervals lengthen safely.
Probability of Recall
The estimated probability that you can successfully recall the information today. Reviews are scheduled at the moment retrievability reaches your target retention rate.
Intrinsic Complexity
How inherently challenging the concept is for your specific brain. High-difficulty cards receive gentler initial interval increases to prevent lapses.
Interactive Preview: FSRS 4-Button Grading Simulator
Test the live card below to see how FSRS computes interval days for Again, Hard, Good, and Easy ratings:
FSRS spaced repetition study flashcards
FluxNote builds atomic question-and-answer flashcards with memory mnemonics directly from your audio recordings. The modern FSRS algorithm calculates your forgetting curve and schedules reviews right before memory fades.
What chemical triggers light absorption in photosynthesis?
Comparing FSRS with legacy SM-2
| Feature | Legacy SM-2 (Anki defaults) | FSRS (FluxNote) |
|---|---|---|
| Total reviews required | Higher (often over-reviews easy cards) | Up to 30% fewer reviews for the same retention |
| Ease Hell problem | Common: hitting 'Hard' permanently shrinks intervals | Eliminated: difficulty and stability scale independently |
| Audio integration | Requires third-party add-ons or manual file linking | Built-in: flashcards link directly to source audio |
| Pre-exam review | Complex filtered decks that risk corrupting schedules | One-tap Cram Mode with zero schedule disruption |
How to rate cards in FluxNote
To get the maximum retention benefit from FSRS, grade your recall honestly:
- Again: Select this if you could not recall the answer, or if you recalled it incorrectly. This resets retrievability and schedules an immediate review.
- Hard: Select this if you reached the correct answer, but it required intense effort or took longer than 10 seconds of searching your memory.
- Good: Select this if you recalled the answer with a normal amount of effort. This should be your most frequent rating.
- Easy: Select this if the card felt trivial or if you knew the answer instantly without pause. This increases stability substantially.