Why does a word you studied yesterday show up again today?
It’s not a random replay — it’s an algorithm called FSRS that schedules your review at the exact moment your memory needs a nudge, so no practice is wasted.
- 01
Forgetting follows a curve
Scientists have found that after learning a new word, you lose memory unevenly — about half is gone within an hour, and only 20% remains a week later. Reviewing everything every day is exhausting; reviewing once a week is already too late.
- 02
FSRS times each review for you
FSRS (Free Spaced Repetition Scheduler) remembers how you responded to every word — instantly correct, hesitated, or completely forgot — and uses that to compute exactly how many days until you should see it again.
Hard words come back sooner; words you know cold get pushed further and further out.
- 03
Three memory states to watch
Every word you’ve studied sits in one of three states. The balance between them is your “memory health” — one glance tells you whether your review pace is healthy.
- Solid
- Need Review
- Fading