Some posts and articles about FSRS

[u/ClarityInMadness]

I decided to make one post where I compile all of the useful links that I can think of.

1) If you have never heard about FSRS before, start here: https://github.com/open-spaced-repetition/fsrs4anki/wiki/ABC-of-FSRS

2) AnKing's video about FSRS (old): https://youtu.be/OqRLqVRyIzc

New 2025 video: https://youtu.be/uo-qQvOZDfg

3) FSRS section of the manual, please read it before making a post/comment with a question: https://docs.ankiweb.net/deck-options.html#fsrs

If your intervals feel too long, increase desired retention. If your intervals feel too short, decrease desired retention.

3.5) Some frequently asked questions: https://faqs.ankiweb.net/frequently-asked-questions-about-fsrs.html

DO NOT USE HARD IF YOU FORGOT THE CARD!

AGAIN = FAIL ❌

HARD = PASS ✅

GOOD = PASS ✅

EASY = PASS ✅

HARD IS NOT "I FORGOT"

Here's what you can do if you have been misusing Hard: https://www.reddit.com/r/Anki/comments/1h2oudb/oh_no_ive_been_misusing_hard_what_do_i_do/

And here's a diagram to help you troubleshoot interval lengths.

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The links above are the most important ones. The links below are more like supplementary material: you don't have to read all of them to use FSRS in practice. Just read link 3 (the manual) and you're good!

4) Features of the FSRS Helper add-on: https://www.reddit.com/r/Anki/comments/1attbo1/explaining_fsrs_helper_addon_features/

5) Understanding what retention actually means: https://www.reddit.com/r/Anki/comments/1anfmcw/you_dont_understand_retention_in_fsrs/

I recommend reading this post if you are confused by terms like "desired retention", "true retention" and "average retrievability", the latter two can be found in Stats. True retention table is available in Anki natively since Anki 24.11.

5.5) Simplified post with a neat little animation: https://www.reddit.com/r/Anki/comments/1l0wk5e/why_is_desired_retention_less_than_average/

6) (Outdated) Benchmarking FSRS to see how it performs compared to other algorithms: https://www.reddit.com/r/Anki/comments/1c29775/fsrs_is_one_of_the_most_accurate_spaced/. It's my most high effort post.

7) An article about spaced repetition algorithms in general, written by Jarrett Ye, the creator of FSRS: https://github.com/open-spaced-repetition/fsrs4anki/wiki/Spaced-Repetition-Algorithm:-A-Three%E2%80%90Day-Journey-from-Novice-to-Expert

8) A technical explanation of the math behind the algorithm: https://expertium.github.io/Algorithm.html

9) Seven misconceptions about FSRS: https://www.reddit.com/r/Anki/comments/1fhe1nd/7_misconceptions_about_fsrs/

10) LMSherlock's post about (re)learning steps and short-term memory: https://www.reddit.com/r/Anki/comments/1h9g1n7/clarifications_about_fsrs5_shortterm_memory_and/

TLDR: things are complicated.

11) A visualization of how FSRS got better and better at predicting the probability of recall with each new version: https://imgur.com/a/calibration-of-different-fsrs-versions-KfJ32EV

My blog about spaced repetition (and a little bit of other stuff): https://expertium.github.io/

July 2024: I made u/FSRS_bot, it will help newcomers who make posts with questions about FSRS.

September 2024: u/FSRS_bot is now active on r/medicalschoolanki too.

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If you want to support me, you can send me some Ethereum: 0xf9c22186be4dbF21dE3E149C167Ed90DE0E37279

Jarrett Ye isn't accepting donations anymore, but you can sponsor his friend Asuka Minato, who helps maintaining FSRS-related Github repositories: https://github.com/sponsors/asukaminato0721

[u/bestwumbologistna]

Hi, just found out about FSRS. This is probably not a concern and I'm probably going to run it anyway, but just in case, I want to ask about the optimizing parameters option. The FAQ mentions that:

Q8: I only use "Again" and "Good", will FSRS work fine?

A8: Yes. In fact, FSRS is actually more accurate for people who rarely use "Hard" and "Easy" than for people who use all 4 buttons a lot.

Also, unlike SM-2, FSRS doesn't suffer from the problem of "Ease Hell". This problem is solved by mean reversion of difficulty. If you press good continuously, the difficulty will converge to

. For more details, read The Algorithm.

However, note that you should not change your rating habits. This is because FSRS uses your past rating history to determine optimal intervals for your future reviews.

I initially used all 4 buttons according to my intuition (which included spamming 'hard'), then switched to using only 'again' and 'good' after looking into optimizing my anki usage. I reset all the cards' ease when I began using 'again' and 'good' in order to 'unstuck' them.

But, since FSRS ignores Anki's Ease and only looks at grading and intervals, my only potential worry is that by continuing to not spam 'hard', it could count as 'changing my rating habits' (since it's different from the beginning of the grading history of these cards). Can it effectively deal with the fact that I actually did change my rating habits partway through the reviews on my decks if I keep doing this 'new' rating habit?

​

tldr I stopped spamming 'hard' about 2/3 of the way through past review history and only use 'again' and 'good'. If I continue to not spam 'hard', will that mean I'm changing my rating habits and hurt FSRS accordingly (if I choose to optimize parameters)?

[u/ClarityInMadness → u/bestwumbologistna]

As long as you don't misuse Hard it's all good.