How does the Readwise spaced repetition algorithm work (Mastery)?

Admittedly, the Readwise spaced repetition algorithm (Mastery) is a bit of a black box compared to powerful spaced repetition software (SRS) such as Anki or SuperMemo. The reason for this is that we're trying to create a spaced repetition alternative that is extremely user friendly compared to the existing offerings, which have notoriously steep learning curves.

That said, here are the full details behind the Readwise spaced repetition algorithm:
  • We use a decaying algorithm based on a recall probability half-life rather than a date-based algorithm as found in Anki.
  • The initial half-life of a Mastery `later` is 14 days. `Soon` is 7 days. `Eventually` 28 days.
  • Once a highlight recall probability decays to 50% or lower, it becomes a candidate to be resurfaced in the latter half of your Daily Review.

If you have a lot of Mastery flashcards that are candidates to be resurfaced (probability of recall less than 50%), then those with the lowest recall probability will be resurfaced in your Daily Review.

You can see all your Mastery flashcards, their half-lives, and recall probabilities here: