How Prior decides when a card comes back

Prior schedules each card with FSRS, a model of memory. What Again, Hard, Good and Easy do, how the retention setting works, and where to check it.

Memory fades with time, and every successful review makes it last longer. Prior tracks this for each card and brings the card back shortly before you would probably forget it. A card you know well comes back after weeks or months. A card you keep missing comes back within days.

#What Prior keeps for each card

Prior uses FSRS, the Free Spaced Repetition Scheduler, in its fifth version with its standard published settings. It does not tune them to your history. For each card it works out three things, which you can read in Card info (press I in a review):

• Stability: how many days it takes for your chance of recalling the card to drop to 90 %. It grows with every successful review.
• Difficulty: how hard this card is for you, from 1 to 10.
• Recall now: your estimated chance of remembering the card today.

The next review is set for the day your chance of recalling it falls to your Target retention.

#What the buttons do

Under each button, Prior shows how long until the card returns, so you can see the effect before you choose.

A card you are learning (a new card, or one you forgot) goes through short steps first. With the defaults, 1 minute then 10 minutes:

• Again goes back to the first step.
• Hard repeats the current step. On the first step it waits about halfway to the next one.
• Good moves to the next step. After the last step, the card joins your regular reviews.
• Easy joins your regular reviews at once, with a longer first interval.

A card in review gets a new interval:

• Again counts as a lapse. The card goes back to a relearning step (10 minutes by default), and its stability drops.
• Hard gives the shortest of the three intervals, and the card counts as harder.
• Good gives the planned interval.
• Easy gives the longest interval, and the card counts as easier.

A review after a long gap teaches more than one right after the last. If you remember a card that had nearly faded, its stability grows more. Intervals longer than about two and a half days also vary a little from card to card, so that cards learned together do not all return on the same day.

#Choose your retention

Target retention is how likely you want to be to remember a card when it returns. The default is 90 %. Set it in Deck settings, from 70 % to 99 %. Higher means more reviews, and lower means fewer reviews and more forgetting.

The effect is large. Compared with 90 %, intervals at 95 % are about half as long, and intervals at 80 % are about two and a half times longer. A deck with a study plan takes its retention from the plan.

Three more settings sit under Advanced: Learning steps (minutes), Relearning steps (minutes) and Maximum interval (days), which caps every interval. The defaults are 1 10, 10 and 36,500.

#Check how it is going

Open a deck's Stats tab:

• True retention is the share of your answers over the last 30 days, to cards you had already learned, that were not Again. It sits next to your target. If it sits far below the target, your cards may be too hard or too vague. See Write better flashcards.
• Next 30 days shows how many reviews are coming.
• Leeches lists the cards you have forgotten 8 times or more. Prior does not suspend them for you. Rewrite them, or choose Suspend.

#Good to know

• The schedule is not stored, it is recomputed. Prior replays your answers in order to work out each card, so two devices that sync always agree, even if you studied offline on both.
• Reset to new. A card can go back to the start from its row menu or from the card browser. Its history stays in the log.
• Late is fine. A card you review after its due date is scheduled from the day you actually answered.

Updated 5 November 2026