If you've ever crammed vocabulary the night before a test and forgotten most of it a week later, you've experienced what psychologist Hermann Ebbinghaus documented over a century ago: memory decays fast, and it decays predictably. His research produced what's now known as the "forgetting curve" — a description of how quickly newly learned information fades without reinforcement.
The fix Ebbinghaus's own research pointed toward wasn't more repetition packed into one sitting. It was spaced repetition: reviewing information at increasing intervals, timed to land right before you're about to forget it.
The core idea
Each time you successfully recall a word, the memory becomes more durable and the next ideal review interval gets longer. Miss a review, and the interval resets shorter. Over time, well-known words get reviewed rarely (because you've proven you remember them), while shaky words come back often — until they're solid too.
This is different from simply "reviewing often." Reviewing a word you already know cold is a waste of a study session; reviewing a word right as it's about to slip away is the single most efficient moment to reinforce it. Spaced repetition systems exist to calculate that moment for every word individually, rather than leaving it to guesswork.
What the forgetting curve actually shows
Ebbinghaus's original experiments had him memorizing nonsense syllables and testing his own recall at intervals afterward. The pattern he found was consistent: the steepest drop in memory happens fast — within the first day — and then the rate of forgetting slows down the longer the memory survives. In other words, the first review after learning something new matters disproportionately. A word reviewed once within a day of first seeing it is far more likely to survive long-term than one left untouched for a week.
This is also why re-reading a word list five times in one sitting feels productive but barely helps — all five repetitions happen before any forgetting has occurred, so there's nothing for the brain to "resist." Real reinforcement happens when you successfully retrieve a memory that was at risk of being lost, not when you passively re-expose yourself to something you still remember clearly.
Why spacing beats cramming, mechanically
The effect behind this has a name in cognitive psychology: the spacing effect. Decades of research since Ebbinghaus have confirmed it across age groups, subjects, and languages — information reviewed at spaced intervals is retained substantially better than the same information reviewed the same number of times in a single session.
The likely mechanism is retrieval difficulty. Recalling a word right after learning it is easy — the memory is fresh, so there's no real retrieval effort involved. Recalling the same word three days later, when it's started to fade, requires your brain to actively search for it. That extra effort is what strengthens the memory. Cramming skips this step entirely, which is why crammed information disappears so quickly afterward — it was never actually retrieved under difficulty, only re-read.
Why this matters especially for German vocabulary
German vocabulary carries extra load compared to many languages — not just the word itself, but its article (der/die/das), plural form, and often a case ending that changes depending on the sentence. That's more information per word to forget, which makes consistent, well-timed review even more valuable than it would be for a language with less grammatical baggage attached to each noun.
This is also why serious language programs, including those built around the CEFR framework used across European language instruction, emphasize consistent, structured review over one-time exposure — the standard assumes learners will revisit material repeatedly as they move through proficiency levels, not master it in a single pass.
What a spaced repetition schedule actually looks like
A typical spaced repetition system doesn't use one fixed interval — it adjusts individually per word based on how well you know it. A rough shape of how intervals grow after each successful recall:
- First review: about 1 day after first learning the word
- Second review: about 3 days after the first review
- Third review: about a week after that
- Fourth review: two to three weeks later
- Continuing to expand as long as recall stays successful
Miss a review or answer incorrectly, and the interval resets to something short again — the system treats that as a sign the memory needs reinforcing sooner, not later. This is what separates spaced repetition from a fixed study calendar: the schedule adapts to you, word by word, rather than treating every word as equally difficult.
Putting it into practice
You don't need to calculate review intervals by hand — that's exactly what spaced repetition software is for. What matters on your end is consistency: reviewing on the schedule the system gives you, rather than skipping days and letting intervals reset. A few minutes of review daily, done on time, outperforms an hour of cramming once a week.
Combined with level-based vocabulary and words learned in real sentence context, spaced repetition is the third piece of what actually makes vocabulary stick — the full method is laid out in how to learn German vocabulary that actually sticks.
LUMO builds spaced repetition into every word card automatically — no manual scheduling required. Download LUMO on the App Store or get one word a day, free, in your inbox.