All tools
FSRS Calculator
See the algorithm behind every review.
Tune stability, difficulty, and desired retention. Watch the next interval update in real time — the same math that schedules every Revu review.
30 days
1 day365 days
How many days can pass before your recall probability drops to 90%.
5 / 10
EasyVery hard
Higher difficulty slows stability growth after correct reviews.
90%
70%95%
Probability of recall at the time of next review. Higher = more reviews.
Review grade
Results
Next review in
35.2days
~1 month
New stability
35.2days
+17% vs current
Retrievability at review
90%
Probability of successful recall when the card reappears
A good response is the standard successful recall. FSRS increases stability based on difficulty and how close you were to forgetting.
Stability
The number of days before your recall probability falls to 90%. Every successful review grows it; a lapse shrinks it.Difficulty
Per-card property (1–10). Higher difficulty slows stability growth. FSRS auto-calibrates from your actual reviews.Desired retention
The lever you control. 70% = long intervals, more forgetting; 95% = short intervals, heavy review load. Sweet spot 85–92%.Revu schedules every card with FSRS — zero config