Spaced repetition means reviewing material at growing intervals: soon after you learn it, then a few days later, then a week, then longer. Each successful review lets you wait longer before the next one. It takes less total time than cramming and holds up far better weeks later. It works best combined with testing yourself.
Why do we forget, and how does spacing help?
Hermann Ebbinghaus described the “forgetting curve” in 1880s experiments on himself, learning lists of nonsense syllables: without review, what he learned faded fast at first and then more slowly. A modern replication, in which one person spent 70 hours learning and relearning lists at delays from 20 minutes to 31 days, produced results very similar to his original data (Murre & Dros, 2015).
Each review resets the curve and makes it flatter. That is why a few well-timed reviews beat many reviews crammed into one night.
In a major review of ten study techniques, distributed practice (spacing) was one of only two techniques rated “high utility”, alongside practice testing (Dunlosky et al., 2013).
What are the best spaced repetition intervals?
The ideal gap depends on how long you need to remember something. In a study of more than 1,350 people (Cepeda et al., 2008) who learned facts, reviewed them after a gap of up to 3.5 months and were tested up to a year later, the best gap got longer as the test got further away. As a share of the time until the test, the best gap fell from roughly 20 to 40 percent for a test one week away to about 5 to 10 percent for a test one year away (Cepeda et al., 2008).
In plain terms:
| You need to remember it for | A reasonable first review gap |
|---|---|
| About 1 week | 1 to 3 days |
| About 1 month | About a week |
| About a year | 3 to 5 weeks |
For ongoing learning, a common schedule looks like this, resetting a card whenever you miss it:
- Day 1: learn it and test yourself once at the end of the session
- Day 2
- Day 4 to 5
- Day 10 to 14
- About a month later
- Two to three months later
Treat these as starting values, not rules.
Why must spaced repetition include testing?
Spacing tells you when to review. How you review matters just as much. Rereading a card’s answer is not the same as producing it. In one experiment, repeated testing after learning had a large positive effect on recall a week later, while repeated studying had none (Karpicke & Roediger, 2008).
So every review should be a small test: see the question, answer from memory, then check. More on this in our active recall guide.
How do you do spaced repetition with paper flashcards?
Use the Leitner system: cards move through a series of boxes. Answer correctly and a card moves to the next box, which you review less often. Answer wrong and it goes back to box 1 (Leitner system).
A five-box version:
| Box | Review |
|---|---|
| 1 | Every day |
| 2 | Every 2 to 3 days |
| 3 | Once a week |
| 4 | Every two weeks |
| 5 | Once a month |
It is simple, it needs no app, and it makes progress visible: you can watch the cards move to the right.
How do you use Anki for spaced repetition?
Anki is a free flashcard app that schedules reviews for you. It offers two scheduling algorithms: one based on SuperMemo’s SM-2 and a newer one called FSRS, which tries to learn your memory patterns and schedule reviews more efficiently (Anki FAQ).
Practical tips:
- Do your reviews every day. Missed days pile up. Ten minutes daily beats an hour on Sunday.
- Limit new cards. 10 to 20 a day is plenty to start. New cards today mean reviews for weeks.
- Answer honestly. If you hesitated or half-knew it, press “Hard” or “Again”. Flattering yourself breaks the schedule.
- Leave the default settings alone at first. Tweak only when you understand what a setting does.
What makes a good flashcard?
| Weak card | Better card |
|---|---|
| “Photosynthesis” | “What are the two main stages of photosynthesis?” |
| A full paragraph on the back | One fact or one short explanation |
| “List all 12 cranial nerves” | Twelve cards, one per nerve, plus one for the order |
| Copied sentence from the textbook | Your own wording |
| Only “what” questions | Some “why” and “how” questions too |
Rules of thumb:
- One idea per card. If you get half of it wrong, you do not know which half.
- Understand before you memorize. Cards for material you do not understand turn into rote noise.
- Add context. A picture, an example, or where it fits in the bigger topic.
- Delete bad cards. A card you keep failing may just be badly written. Rewrite it.
How do you fit spaced repetition into a study week?
Keep daily reviews short and separate from learning new material:
| When | What |
|---|---|
| Start of each study day | One 25-minute block of reviews (cards that are due) |
| Middle | New material: lectures, reading, problem sets |
| End of the session | Make cards for today’s material; test yourself once |
| Weekly | Blank-page review of one older topic |
A 25/5 timer works well for the review block: if all due cards are done early, stop. If not, finish them in the next block.
What are the most common spaced repetition mistakes?
- Adding too many cards too fast, then abandoning a backlog of hundreds of reviews.
- Only using it the week before exams. Spacing needs time to work.
- Making cards instead of studying. Card creation should be quick.
- Never pruning. Cards for material you no longer need still cost time.
Start today
Pick one topic from this week, write ten question cards, test yourself once, and schedule the first review for tomorrow.