RemNote's default flashcard scheduler is called Anki SM-2. As the name suggests, it is based on the scheduling algorithm used by the popular flashcard software Anki, with minor changes intended to maximize your long-term learning.

This article explains the technical details of Anki SM-2. For information on how to change the scheduler used for particular flashcards or an entire Knowledge Base, see our article on Custom Schedulers. If you're interested in a first-principles explanation of why the algorithm was built this way, check out Spaced Repetition from the Ground Up (this post is not written by RemNote and is not specific to RemNote's implementation of SM-2).

Throughout the remainder of this article, phrases in italic type refer to scheduler parameters found in the “Custom Schedulers” section of RemNote's settings.

The initial Learning Phase is designed to help you quickly internalize new ideas. In the Learning Phase, flashcards pass through a series of steps of a fixed length, determined by the Initial Learning Phase Fixed Steps parameter. (An interval is the number of days between consecutive reviews of a card.) For example, if you enter 30m,2h,2d in this field, the card will proceed through steps of 30 minutes, 2 hours, and 2 days.

During this phase:

You can achieve steps of less than 1 day by using h or m for hours or minutes in place of d.

Note: When you reach the end of the queue, cards in the Learning Phase may be shown for practice a few minutes before they become due. To understand why, consider what happens if you finish your queue 5 seconds before a difficult card in the Learning Phase, with a current interval of 10 minutes, becomes due. You likely will not return to your queue for at least several hours, or maybe even several days, since you expect very few cards to become due, making it significantly more likely that you’ll forget this card.

It is clearly less bad to see a card that you’re only barely remembering 5 seconds early than to see it a day late, so that's what RemNote does. You can customize the amount of time RemNote will allow learning cards to be displayed early using the Learn Ahead Limit option in Settings > Flashcards; the default is 15 minutes.

The Exponential Phase is the main study phase where cards spend most of their lives. Intervals in this phase increase exponentially (by multiplying the previous interval by some number). The number multiplied by is called the Interval Factor, and it's calculated for each card every time you practice it.

The Interval Factor is determined by two figures: the card's ease (a measure of how difficult you've found the card in the past), and the rating button you select (Forgot, Partially Recalled, Recalled with Effort, or Easily Recalled). Each card's ease begins at the Starting Ease setting (230% by default) and is updated every time you practice the card. In other flashcard apps, the ease is sometimes called the E-Factor.

The ease and Interval Factor are calculated in the Exponential Phase as follows:

The Interval Factor is then adjusted further:

The Interval Factor is then used to calculate the card's next interval. In most cases, the next interval is simply the current interval times the Interval Factor. However, if the card is being reviewed late (after the date it would optimally be reviewed on), and you answered something other than Forgot, a bonus of (Days Late / Hardness Divider) is added to the card's current interval before multiplying. The Hardness Divider is 4 for Partially Recalled, 2 for Recalled with Effort, and 1 for Easily Recalled.

Why include this bonus? Suppose RemNote thinks you needed to review the card on some particular day, but actually you don't review it until 10 days later, and you still remember the answer. This means you actually know the card better than RemNote originally thought you did, and the better you know a card, the longer you can wait between reviews, so the interval should grow somewhat more than it would have otherwise (or a lot more, if it's been a very long time). The Hardness Divider adjusts this amount of increase for how well you believe you still remembered the card; if you really struggled to still remember it, it makes sense for the increase to be less than if you still found it trivially easy.

A card's ease can in no circumstances be reduced to less than 130%; if the calculations discussed above would reduce it to less than 130%, the ease is set to 130% instead. Experience has shown that if a card would naturally require an ease of less than 130% to remember reliably, it is too difficult for effective spaced-repetition study and should instead be improved in some way (by writing it more clearly, developing a mnemonic, or some similar approach). Showing the card more often ordinarily leads to frustration and little to no benefit to memory.

When you forget a card during the Exponential Phase, it enters the Relearning Phase. This phase works very similarly to the initial Learning Phase; cards proceed through a series of fixed steps and return to the Exponential Phase when these fixed steps are complete, or when you press Easy.

The main difference in the Relearning Phase is that, rather than calculating the card's initial interval in the Exponential Phase based on the last review of learning/relearning, the card's last interval during its previous sojourn in the Exponential Phase is used. The new interval will be equal to this last interval times the Lapse Interval Multiplier (by default 0.1, so that the new interval will be a tenth of the old one).