Why hasn't the recall changed after adjusting the Forget Index?

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Why does my daily recall remain above 90% even after adjusting the Forget Index to 20? I understand that the sm-18 algorithm doesn't review exactly according to the given FI, instead offering a longer interval, but shouldn't this result in a recall rate slightly below 80%? This is especially puzzling considering there wasn't a significant change in my recall rate before and after adjusting the FI. I started adjusting the FI to 20 in February this year, and at the same time, I adjusted the FI of all items to 20, meaning the average FI of the entire collection is 20. Before this change, my monthly average recall was still above 90%, and it remained above 90% afterwards as well. Is this normal?


If you change the forgetting index in Options the impact is not immediate. The lag depends on the average interval of items affected


  • default FI for a concept is inherited from the currently used concept or from a category defined in earlier SuperMemos (and upgraded to a concept)
  • in a new collection, default FI for a concept is the same as global default set in Options
  • manually setting FI to zero will make it equal the global default
  • default FI for a concept cannot be set in the concept registry (in SuperMemo 19). It is recommended to use default priority instead (priorities determine the degree of forgetting in overload)
  • changing the value of the FI is not recommended or necessary. Decreasing FI (increasing retention) may go against the art of learning (except for some potential mission critical items). Increasing FI (e.g. to 20%) allows of higher speed of learning, but this can better be accomplished by adding more material (i.e. overload). Even if the goal is to keep a minimum time for spaced repetition, priority queue and "neglect" might work better


(please come back in a few days for details)