How Sogda remembers
Spaced repetition with FSRS, explained
Sogda plans every revision with FSRS-4.5, a spaced-repetition method that brings each word back on the day your chance of recalling it would drop to 90%. A new word you rate Good comes back after 4 days, then after 15, 50 and 150 days as you keep rating it Good, so your minutes go to the words you're about to forget.
What FSRS is
FSRS, the Free Spaced Repetition Scheduler, is an open-source method for deciding when to revise. For each word it tracks how stable your memory of it is and how hard the word is for you, and from those it works out the day your chance of recalling it would drop to your target. Sogda runs FSRS-4.5 with its published default weights, on your phone.
Your target is 90% unless you change it: Target retention in Settings goes from 80% to 97%. A higher target brings words back sooner, so there are more revisions a day; a lower one spaces them further apart.
The first gap depends on your rating
When a new word comes up, you rate how well you knew it with the app's four buttons. At the default target, the rating sets its first gap:
- Again: back in 1 day
- Hard: back in 1 day
- Good: back in 4 days
- Easy: back in 14 days
Then the gaps grow
Each time the word comes back and you rate it Good, your memory of it is more stable and the next gap is longer: 4 days, then 15, 50 and 150, and after that 409 days, more than a year.
Forget a word you'd learned and rate it Again, and FSRS lowers its stability: the word comes back sooner, and its gaps grow again from there.
Revision comes first, every day
Each day's plan starts with revision: the words that are due, the earliest first, up to 10 of them. When fewer are due, it fills the rest with the words you're most likely to have forgotten. Then come 7 new words, the grammar that's due and a few practice sentences.
Both numbers are defaults you can change in Settings. Due words beyond the day's 10 wait for the next day, the earliest first, so a missed day never turns into a wall of revisions.
Why your minutes go to the words you're about to forget
A word you know well is planned weeks or months ahead, so it takes none of today's time. A word that's fading is planned now, just before you'd forget it. The minutes you have each day go to the words that need them, and each revision you pass pushes the next one further out.
Questions, answered.
Can I change how often words come back?
Yes. Set Target retention in Settings, from 80% to 97%; the default is 90%. A higher target means shorter gaps and more revisions a day; a lower one, longer gaps and fewer.
What happens if I miss a day?
The words that were due wait for you. The next day's plan takes the earliest due first, up to 10 revisions, and the rest follow on the days after. When you rate a word, FSRS counts the days that really passed.
Does the scheduling need the internet?
No. Sogda works fully offline: the scheduler runs on your phone, with no account, and your progress stays there.
Does Sogda schedule grammar too?
Yes. Each grammar topic has its own schedule from the same scheduler, and comes back for practice when it's due.