What Is Spaced Repetition and Why Does It Work?
If you have ever crammed for a test only to forget everything a week later, you already know the limits of massed practice. Spaced repetition is the antidote: a study technique that spaces your reviews over increasing intervals to move information from short-term to long-term memory.
The Spacing Effect
In 1885, German psychologist Hermann Ebbinghaus discovered that we forget new information at a predictable rate — the famous forgetting curve. He also found that reviewing material at strategic intervals dramatically slows that forgetting. This is the spacing effect, and it has been replicated in hundreds of studies since.
The key insight is simple: the best time to review something is right before you are about to forget it. Review too early and you waste time. Review too late and you have to relearn from scratch.
How Spaced Repetition Systems Work
A spaced repetition system (SRS) automates the scheduling of reviews. Here is the basic loop:
- You learn a new item (a vocabulary word, a fact, a concept)
- The system schedules your first review — usually the next day
- When you review, you rate how well you remembered
- Based on your rating, the system adjusts the next review interval
- Easy items get pushed further out; hard items get reviewed sooner
Over time, well-known items might not come up for weeks or months, while difficult items appear frequently until they stick.
Why FSRS Is Different
MassVocabulary uses the Free Spaced Repetition Scheduler (FSRS), a next-generation algorithm developed by Jarrett Ye and published as peer-reviewed research. FSRS improves on older algorithms like SM-2 (used by Anki) in several ways:
- Adaptive to you: FSRS models your personal memory patterns, not just a generic curve
- Fewer wasted reviews: by predicting your recall probability more accurately, FSRS avoids unnecessary reviews
- Better long-term retention: studies show FSRS achieves higher retention rates with fewer total reviews compared to SM-2
- Open and transparent: the algorithm is open-source and backed by published research
Applying This to Vocabulary
Vocabulary is one of the best use cases for spaced repetition because languages contain thousands of discrete items (words) that need to be memorized independently. MassVocabulary combines FSRS with contextual learning — you review words within example sentences, so you build both recognition and the ability to use words naturally.
Getting Started
The most important thing is consistency. Even 10 minutes a day with spaced repetition is more effective than an hour of cramming once a week. MassVocabulary tracks your optimal daily load and shows you exactly what to review each day, so you can build a sustainable habit.
Want to experience spaced repetition for yourself? Try the interactive demo on our homepage or join the beta waitlist to get early access.