Spaced Repetition Schedule: Day 1, 7, 21, 60

The best spaced repetition schedule for most material is four reviews: on day 1, day 7, day 21 and day 60 after you first study it (day 0). That keeps material for six months or more with about five short sessions in total. If you need it for a shorter time, shrink the gaps. The table below gives a schedule for each deadline.

The gaps are not arbitrary. They follow the largest study of review timing to date, covered below. If you're new to the idea, what spaced repetition is and why it works covers the basics. This page is about timing.

How many days between spaced repetition reviews?

Start with one day, then roughly triple each gap: 1 day, about 1 week, about 3 weeks, about 2 months. The first gap is short because forgetting is fastest in the first 24 hours. Later gaps can be longer because each successful review slows forgetting. If you fail an item, shorten its next gap back to a day or two.

How often should you do spaced repetition?

Review once a day if you use flashcard software, because the software decides which cards are due. A short daily session stops reviews piling up. Without software, you don't need daily sessions. Review each topic only on its scheduled days: the day after you study it, a week later, three weeks later and about two months later.

What are the best spaced repetition intervals?

The best interval depends on how long you need to remember something. In a study of over 1,350 people, Cepeda et al. (2008) found the best gap before a review was about 20% of the time until the test when the test was a few weeks away. That fell to about 5% when the test was a year away. Day 21 sits close to the best single gap for anything from two months to a year.

When to start before a test, and how much to study

There is no fixed number of hours. Plan in sessions instead: one first study and three or four reviews per topic. Reviews are shorter than the first study because you are only retrieving and fixing gaps. To fit the day 1, 7 and 21 reviews in, start a topic at least three weeks before the test. Four to eight weeks gives you room for every topic. Spreading the same hours over more days beats adding hours at the end (Cepeda et al., 2006).

Plan backwards from your deadline

Count days from your first study session (day 0). Pick the row that matches how long you need the material.

Two rules sit behind every row:

• The main gap grows with the deadline, but not in proportion. For a test a few weeks away, the best gap is about a fifth of the time available. For a year away, it is about a twentieth. That is why the 1-year row reaches its main review at around day 25, not day 70.
• Late is better than early. Cepeda's data showed that a gap a little too long cost much less than a gap too short. If you're unsure, wait an extra day or two.

To lay this out across several topics at once, the study planner builds the review sessions into a weekly timetable for you.

What the research says about review timing

The spacing effect. Cepeda, Pashler, Vul, Wixted and Rohrer (2006) analysed 839 comparisons from 317 experiments in 184 articles. Spreading study out beat cramming it into one session. A longer retention period needed a longer gap.

The optimal gap. Cepeda, Vul, Rohrer, Wixted and Pashler (2008) taught more than 1,350 people a set of 32 obscure facts. Each person reviewed the facts once, after a gap of up to 3.5 months, then took a final test up to a year later. For recall, the best gaps were:

At the best gap, final recall was 64% higher than with no gap, for the same study time. This is where the "10–20% rule" comes from. It holds for tests a few weeks to a few months away, but not for a year.

What to do at each review. Dunlosky et al. (2013) rated practice testing and distributed practice the two most useful study techniques of the ten they reviewed, and rated re-reading low. So each review should make you retrieve the answer from memory, not re-read.

The calendar method

The most common way a schedule fails is forgetting to review. Fix that on day 0:

1. Study the material.
2. Open your calendar straight away.
3. Add review events for day 1, day 7, day 21 and day 60.
4. At each review, recall from memory for 10–15 minutes, then check your notes.

If a review shows you've lost several items, add an extra review three days later and carry on with the schedule from there.

How Anki schedules your reviews

Anki works out the gaps for you. In its default scheduler (SM-2), each card has an ease value that starts at 2.5. When you answer Good, the next interval is roughly the last one multiplied by the ease, so a 10-day interval becomes about 25 days. Pressing Hard or Again shortens the interval and lowers the ease. Pressing Easy lengthens it.

Since version 23.10, Anki also offers FSRS, an optional scheduler that sets intervals by estimating how fast you personally forget each card. Either way, the gaps grow in roughly the same pattern as the schedule above, adjusted to how well you actually recall.

What happens when you skip a review

Missing one review rarely does serious damage. The item will be harder to recall, but most of it is usually still there. The real danger is skipping in a cascade: one missed day becomes three, and the reviews pile up.

If you miss a review:

• One or two days late: do it now and keep the next date as planned. A slightly late review still works, as the research above shows.
• A week or more late on material you've reviewed once or twice: treat it as a new first study and restart from day 1.
• Back from a long break: review your most recent material first, then work back through the older topics.

A 10-minute session on a bad day beats skipping and catching up later.

The review session itself

1. Cover the answer. Turn the card over or close your notes.
2. Try to recall it. Produce the answer completely from memory.
3. Check. Compare what you produced with the source.
4. Rate it. In Anki use Again/Hard/Good/Easy. On paper, mark pass or fail.
5. Move on. Don't linger on what you got right. Spend the time on what you missed.

Build a deck and try it

Pick 20–30 facts you're studying now and follow the day 1, 7, 21 schedule for a month. Use the flashcard maker to build the deck in your browser and review it in focus mode. Then use the study planner to put the review days into your week. The free Spaced Repetition course covers the forgetting curve and the SM-2 algorithm in more depth.

References

• Cepeda, N. J., Pashler, H., Vul, E., Wixted, J. T., & Rohrer, D. (2006). Distributed practice in verbal recall tasks: A review and quantitative synthesis. Psychological Bulletin, 132(3), 354–380.
• 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.
• Dunlosky, J., Rawson, K. A., Marsh, E. J., Nathan, M. J., & Willingham, D. T. (2013). Improving students' learning with effective learning techniques. Psychological Science in the Public Interest, 14(1), 4–58.
• 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.
• Anki Manual: Deck Options.