ankiR (version 0.6.0)

fsrs_retrievability: Calculate retrievability for FSRS cards

Description

Computes the current probability of recall using the FSRS-6 power forgetting curve formula. This is the formula used by Anki 24.11+ with FSRS-6.

Usage

fsrs_retrievability(stability, days_elapsed, decay = 0.5)

Value

Retrievability (R), probability of recall between 0 and 1

Arguments

stability

Stability (S) in days - time for R to drop from 100% to 90%

days_elapsed

Days since last review (t)

decay

Decay parameter (w20). In FSRS-6, this is optimized per-user, typically between 0.1-0.8. Default 0.5 is FSRS-4.5 value. Use per-card decay from anki_cards_fsrs() for best accuracy.

Details

The FSRS-6 forgetting curve formula is: $$R(t, S) = (1 + factor \cdot t / S)^{-decay}$$ where factor = 0.9^(-1/decay) - 1.

When t = S, retrievability equals 90% by definition.

Examples

# Card with 30-day stability reviewed 15 days ago
if (FALSE) {
fsrs_retrievability(stability = 30, days_elapsed = 15)
}