Your memory does not decay at a constant rate. It drops fast at first, then slows. Spaced repetition exploits that curve.
The forgetting curve
Learn a word today and you will have lost most of it within a few days — unless you meet it again. Each successful review flattens the curve, and the next review can wait longer.
What that means in practice
| Review | Typical interval |
|---|---|
| 1st | 1 day |
| 2nd | 3 days |
| 3rd | 1 week |
| 4th | 3 weeks |
| 5th | 2 months |
The intervals are not magic numbers; they adapt to how easily you recalled the word. A word you hesitated on comes back sooner.
Why it feels harder than rereading
Because it is. Retrieval — pulling the word out of your memory — is more effortful than recognising it on a page, and that effort is precisely what makes it stick. If your reviews feel comfortable, they are probably too frequent.
The only rule
Do the reviews when they are due. A spaced repetition system that you check twice a week is just a vocabulary list.