Spaced Repetition for Language Learning: Never Forget a Word Again

The Forgetting Curve (And Why Your Vocabulary Keeps Disappearing)

In 1885, German psychologist Hermann Ebbinghaus sat alone for months, memorising and re-memorising thousands of nonsense syllables. From this unusual experiment he derived the forgetting curve: a mathematical description of how quickly newly learned information fades from memory.

His finding: without reinforcement, we forget approximately:

50% of new information within 1 hour
70% within 24 hours
90% within 1 week

If you've ever studied vocabulary for a Spanish exam on Tuesday and found yourself blanking on the same words by Thursday, you've experienced the forgetting curve in action.

The good news: Ebbinghaus also discovered the solution.

What Is Spaced Repetition?

Spaced repetition exploits a quirk of human memory: each time you successfully recall a piece of information, it becomes harder to forget. The memory trace strengthens, and the interval until you need to see it again lengthens.

The algorithm works like this:

You learn a new word (e.g. aprovechar = to make the most of)
You review it tomorrow
If you remember it: review again in 3 days
Remember again: 8 days
Again: 21 days, then 60 days, then 6 months…

The result: you're reviewing words just before you would forget them — no earlier, no later. This is dramatically more efficient than re-reading your vocabulary list every day (which wastes time on words you already know) or waiting until an exam (by which point most words are gone).

SM-2 vs FSRS: Why the Algorithm Matters

For 20 years, the standard spaced repetition algorithm was SM-2, created by Piotr Woźniak in 1987 and popularised by Anki. SM-2 works — it's used by millions of language learners and has strong research support.

But SM-2 has limitations. It uses a fixed "ease factor" for each card that only adjusts slowly, meaning it can over-schedule words you know well or under-schedule words you keep forgetting. It also doesn't model individual forgetting rates: someone with a strong visual memory and someone with a poor verbal memory get the same schedule.

FSRS (Free Spaced Repetition Scheduler), developed in 2022, addresses these limitations:

Models your individual forgetting rate per card, not a global ease factor
Uses a "desired retention" parameter — you can set whether you want 85% or 95% recall and the algorithm adjusts accordingly
Dramatically reduces the number of reviews needed for the same retention level
Studies comparing SM-2 and FSRS show FSRS requires ~15–25% fewer daily reviews for equivalent retention

For practical language learners, this means less time reviewing old words and more time reading new content.

Why Context Makes Vocabulary Stick Longer

Not all vocabulary learning is equal. There is a significant difference between:

Learning aprovechar from a flashcard that says "aprovechar = to make the most of"
Learning aprovechar from a sentence: "Hay que aprovechar el tiempo libre — debes aprender a descansar"

Research in cognitive linguistics shows that contextual encoding creates multiple memory hooks: you encode the word's meaning, its grammatical pattern, the emotional tone of the sentence, and the surrounding narrative. When you try to recall the word later, any of these hooks can trigger the memory.

Words learned from a list are encoded with a single hook: the translation pair. Remove the translation and the word is gone.

This is why combining reading with spaced repetition is so much more effective than using flashcards alone. Your reading session creates the context. Your SRS session reinforces the memory at the right interval. They compound.

Building the Daily Habit

Spaced repetition only works if you actually do the reviews. Here are the habits that make it sustainable:

Keep your daily review session under 15 minutes. If your queue is consistently over 15 minutes, your daily new-card limit is too high. Reduce it.

Review at the same time every day. The habit cue matters more than the time. Before breakfast, during a commute, after coffee — pick one and stick to it.

Don't add more words than you review. Every word you add creates future reviews. Adding 50 new words per day while reviewing 30 creates a debt that will eventually bury you.

Don't skip. Missing one day doubles the chance of missing the next. Missing three days in a row means 70%+ of your cards are overdue. The streak is not a game mechanic — it's a commitment device.

How Volpora Uses FSRS

Volpora saves words automatically as you read — tap a word to translate, and it goes into your personal vocabulary deck. Reviews are scheduled using the FSRS algorithm, calibrated to an 85% default retention target.

Because every word in your deck came from a real sentence in a book you're reading, the contextual hook is already built in. The app shows you the original sentence as the review prompt, not just an isolated translation pair.

The result: you spend less time on SRS reviews than with a traditional flashcard system, and more time reading — which creates new words to learn. The loop feeds itself.

Volpora is available free on Google Play. Your vocabulary deck is built automatically as you read.