kernHow Much of That Book Is Still in Your Head?
You spent about ten hours reading it. Say roughly when you finished, and watch what has happened to it since.
The last book you finished (optional)
When did you finish it?
Still with you
13%
About 1.3 of those 10 hours survived.
Gone
87%
Not lost all at once — it drained out steadily, most of it in the first fortnight.
This is an illustrative model, not a measurement of you. It follows the shape Hermann Ebbinghaus first plotted in 1885 — steep loss early, a long shallow tail, and a small residue that stays for good. Your real number depends on the book, how much you cared about it and what you did afterwards. The shape, though, is not in dispute.
The fix isn't reading it again
Re-reading feels productive and does almost nothing. What moves the green line is retrieval — being asked, and having to dig the answer out yourself. That is all a Kern card is.
Kern does this for books you've actually read
Add a book you finished and Kern writes cards from its ideas, then brings them back right as they start to slip. No highlights, no uploads, no account.
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