FSRS simulator underestimates the number of cards memorized

Anki FSRS
1

The FSRS simulator seems to fail at calculating the number of cards memorized with large decks.

Steps to reproduce

  1. Generate a deck of 6000 basic notes.
  2. Make a default preset for that deck (with the exception of 9999 reviews limit and turning on FSRS).
  3. Run the simulator.

Expected behavior

After ~365 days one would expect to have memorized all 6000 cards at 20 cards per day.

Actual behavior

The simulator estimates ~5700 cards memorized after about 300 days. Counterintuitively, increasing the days to simulate to 3650 makes the estimated number decrease to around 5680.

Debug info

AnkiDroid Version = 2.23.0alpha5 (248e715ff437c50a407d71c119b1f5b735ee2034)  
Backend Version = 0.1.62-anki25.09.2 (25.09.2 3890e12c9e48c028c3f12aa58cb64bd9f8895e30)  
Android Version = 13 (SDK 33)  
ProductFlavor = full  
Device Info = Xiaomi | POCO | mondrian | mondrian_global | 23013PC75G | qcom  
Webview User Agent = Mozilla/5.0 (Linux; Android 13; 23013PC75G Build/TKQ1.220905.001; wv) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/140.0.7339.209 Mobile Safari/537.36  
ACRA UUID = b9d03d9a-5af9-4e67-987e-cc15799171e2  
FSRS = 5.1.0 (Enabled: true)  
Crash Reports Enabled = true
2

300*20*0.95=5700
0.95 - Average retention with 90% Desired retention. This figure is just a rough estimate.

1 Like
3

I guess you’re right, but it’s not intuitive.

4

That would work if the metric were for how many cards you had “introduced” – but introducing them does not automatically mean that every card is “memorized” or known at any particular moment. It would be misleading for the simulator to claim more than Anki/FSRS can provide.

2 Likes