A spaced repetition schedule is the set of gaps between reviews of the same item: you review it, wait, review it again after a longer wait, and so on. You can follow a fixed schedule by hand, such as 1, 3, 7 and 14 days, or let an algorithm choose each gap for each card. This guide explains both, what the research says about how wide the gaps should be, and how to choose.
Key takeaways
- A spaced repetition schedule is a plan for when to review each item, with gaps that usually grow after each successful review.
- The best gap depends on how long you need to remember: a longer horizon allows longer gaps.
- A manual ladder such as 1, 3, 7, 14, 30 days is a reasonable starting template, but it is an illustration, not a research-derived optimum.
- An algorithm like FSRS sets a separate gap for every card based on how you have done on it.
- Whatever you choose, make the first review easy to do, and keep to the schedule.
What a schedule does
Memory fades after learning, then more slowly, as described in the forgetting curve. A review resets the fade, and a well-timed review makes the memory last longer before the next one is needed. The schedule is just the timing of those reviews. The wider idea is covered in what spaced repetition is and why it works.
What the research says about gap size
Cepeda and colleagues taught more than 1,350 people a set of facts, reviewed them after gaps of up to 3.5 months, and tested them up to a year later (Spacing effects in learning: a temporal ridgeline of optimal retention, Psychological Science, 2008). Raising the gap first improved final performance and then gradually lowered it. The best gap grew with the test delay, but shrank as a share of it: about 20 to 40 percent of a one-week delay, down to about 5 to 10 percent of a one-year delay.
Karpicke and Roediger (Journal of Experimental Psychology: Learning, Memory, and Cognition, 2007, vol. 33, issue 4, pp. 704-719) compared expanding gaps with equal gaps. Expanding retrieval practice gave better recall ten minutes after learning, but equally spaced retrieval gave better recall two days later. They also found that delaying the first test, which makes the first retrieval harder, improved long-term retention however later tests were spaced. The practical reading: do not obsess over the exact shape of the ladder, but do not make the first review too soon or too easy.
A manual schedule
If you track reviews on paper or in a spreadsheet, a simple ladder is enough to start. The gaps below are an illustration of the idea, not a measured optimum.
| Review | Gap after the previous one |
|---|---|
| 1st | 1 day |
| 2nd | 3 days |
| 3rd | 7 days |
| 4th | 14 days |
| 5th | 30 days |
If you miss a card at any step, send it back to the start of the ladder. This is the same promote-or-demote logic as the paper boxes in the Leitner system. It works for a small deck. It gets heavy once you have hundreds of cards, because every card sits on its own date.
An algorithm-set schedule
A scheduling algorithm tracks each card separately. The older SM-2 method uses a fixed multiplier adjusted by an ease number; FSRS models the card's memory state instead. The differences are laid out in FSRS vs SM-2.
In FSRS, stability is the number of days it takes the chance of recall to fall from 100 percent to 90 percent (ABC of FSRS). If you set your desired retention at 90 percent, the next review lands about when predicted recall hits that target, so the gap tracks the card's stability. Raise the target and the gaps shrink and the workload rises; lower it and the opposite happens. Desired retention in FSRS explains the trade-off, and what FSRS is explains the model.
Manual or algorithm?
| Manual ladder | Algorithm (FSRS) | |
|---|---|---|
| Setup | None | An app |
| Fits each card | No, same ladder for all | Yes, per card |
| Works with hundreds of cards | Gets heavy | Handled for you |
| Good for | A small deck, a short project | A growing library, long-term goals |
Scheduling for a deadline
If you have a fixed date such as an exam, work backward from it and let the gaps widen as it approaches. The full plan is in how to study for an exam with spaced repetition. For a general-purpose approach to the whole topic, see how to memorize anything.
Using Cirello for scheduling
Cirello schedules every card with FSRS-6, refits the parameters to your own history once you have enough reviews (at least 1,000), and shows only what is due. You do not manage dates by hand. Read about the FSRS app or the broader flashcard app page. The beta is free.
Written by the Cirello team; see about Cirello and how we write for our editorial approach. Questions or corrections? Contact us at [email protected] or through the support page.
Sources
- Cepeda, N. J., Vul, E., Rohrer, D., Wixted, J. T., & Pashler, H. (2008). Spacing effects in learning: a temporal ridgeline of optimal retention. Psychological Science, 19(11), 1095-1102. PubMed
- Karpicke, J. D., & Roediger, H. L. (2007). Expanding retrieval practice promotes short-term retention, but equally spaced retrieval enhances long-term retention. Journal of Experimental Psychology: Learning, Memory, and Cognition, 33(4), 704-719.
- FSRS project wiki: ABC of FSRS