How Spaced Repetition Actually Works (and Why We Built WurdzRus Around It)

In 1885, the German psychologist Hermann Ebbinghaus ran a famously tedious experiment on himself: he memorized lists of nonsense syllables, then measured how quickly he forgot them. The result was the forgetting curve — memory decays exponentially, with most of a new fact evaporating within days.

But Ebbinghaus found something else: each time he relearned a list, it decayed more slowly. Every successful recall flattens the curve.

That observation is the entire foundation of spaced repetition.

The two rules of remembering

1. Review just before you forget. A review that comes too early is wasted effort; one that comes too late is relearning from zero. The sweet spot is the moment the memory is weak but recoverable — and retrieving it then strengthens it far more than re-reading ever does.
2. Stretch the interval after every success. If you recalled a word after 1 day, try 3. Then 7. Then 16. Each successful retrieval earns a longer interval, because the memory is more durable.

This is why cramming fails so predictably: ten reviews in one evening all land on the same point of the forgetting curve. Ten reviews spread across a month intercept ten different points — and each one makes the next decay slower.

How WurdzRus schedules your words

WurdzRus implements SM-2, the algorithm popularized by SuperMemo in the late 1980s and still the backbone of tools like Anki. Every word in your collection carries three pieces of state:

• an ease factor (how hard this word is for you),
• an interval (how many days until you should see it again), and
• a next review date.

Every game you play — hangman, scramble, matching, crossword, spelling — feeds a review event into the same pipeline. Recall the word correctly and the interval grows; fumble it and the interval shrinks. Words that sustain an interval of 21 days or more graduate from learning to learned — that’s the moment the golden gear in your navigation bar ticks up.

No separate flashcard deck, no review queue to dread. The games are the reviews.

The takeaway

You don’t need a better memory; you need better timing. A word reviewed at the right moment five times is worth more than a word re-read fifty times in a weekend.

If you want to feel the difference, take a word you keep forgetting and let the algorithm schedule it. Three weeks later you’ll wonder why it ever seemed hard.