ProfeQuino / Spaced Repetition Explained
Spaced Repetition Explained
The short answer. Spaced repetition means reviewing the same material several times with growing gaps in between, instead of studying it all in one go. A practical schedule is: learn it on day 1, recall it on day 3–4, again on day 7–10, again around day 21, then every few weeks until the exam. Each review must be a recall attempt (answering from memory), not a re-read. It works because a little forgetting makes the next retrieval harder, and that effort makes the memory last. Distributed practice is one of only two techniques rated "high utility" by Dunlosky et al. (2013).
Most students don't need more hours. They need the same hours at better moments. That's what spacing gives you.
What spaced repetition is
Spaced repetition (researchers call it distributed practice) is a way of timing your study. Instead of three hours on one topic on Sunday, you spend one hour on Sunday, one on Wednesday and one the following week. Same total time, very different result.
| Massed (cramming) | Spaced |
|---|---|
| One long session on a topic | Several shorter sessions on different days |
| Feels intense and effective | Feels like "I've forgotten it already!" |
| Great tomorrow, mostly gone in a month | Lasts for months |
| Review is easy (it's still fresh) | Review takes effort, which strengthens memory |
Why the gap helps
When you review something a few minutes after studying it, the answer is still sitting in your head, so retrieval is effortless and adds little. After a gap, you've partly forgotten it. Pulling it back out takes effort, and that effort is what strengthens the memory. Psychologist Robert Bjork called this kind of helpful struggle a desirable difficulty: something that makes learning feel slower now but makes it stick far better later.
The key word is desirable. If you've forgotten everything, the gap was too long and you need to re-learn. If you remember everything easily, it was too short. The sweet spot is: "I got most of it, with effort."
The forgetting curve (illustrative)
In 1885, Hermann Ebbinghaus measured his own forgetting and drew the first forgetting curve: memory drops fast at first, then more slowly. A modern replication found almost the same shape (Murre & Dros, 2015).
Here's the useful part: each time you successfully recall something after a gap, the curve flattens. You forget more slowly, so you can wait longer before the next review.
| Days after learning | No review (illustrative) | With reviews on day 1, 3, 7 and 21 (illustrative) |
|---|---|---|
| Day 1 | Drops steeply | Recalled, back near the top |
| Day 3 | A fraction remains | Recalled again, decays more slowly |
| Day 7 | Mostly gone | Recalled, curve flatter still |
| Day 21 | Very little left | Recalled, now stable for weeks |
This table describes the typical shape of the curves, not data from a single study. Exact numbers depend on the material, the person and how well it was learned.
The evidence
| Study | What they found |
|---|---|
| Cepeda et al. (2006), Psychological Bulletin | A meta-analysis of 839 assessments from 317 experiments: spaced practice beat massed practice across materials and retention intervals |
| Cepeda et al. (2008), Psychological Science | Over 1,350 people, gaps up to 3.5 months, tests up to a year later. The best gap depends on how long you need to remember: roughly 20–40 % of the time to the test for short horizons, falling to about 5–10 % for a year |
| Kornell (2009), Applied Cognitive Psychology | With flashcards, spacing beat cramming for about 90 % of participants, yet 72 % believed cramming had worked better |
| Donoghue & Hattie (2021), Frontiers in Education | Across 242 studies, distributed practice had the largest effect of ten techniques (d = 0.85) |
| Dunlosky et al. (2013) | Distributed practice rated high utility, alongside practice testing |
That Kornell result is the one I show students: spacing works for almost everyone, and almost everyone thinks it doesn't. Don't trust the feeling; trust the results a week later.
Recommended intervals
The default expanding schedule
| Review | When | What you do |
|---|---|---|
| 0 | Day 1 | Learn it, then do an immediate recall loop |
| 1 | Day 3–4 | Recall from scratch, check, fix the gaps |
| 2 | Day 7–10 | Recall again, ideally mixed with other topics |
| 3 | Day 21 | Recall, or answer a past-paper question on it |
| 4+ | Every 4–6 weeks | Until the exam; lengthen the gap if it's solid |
If the exam is closer
| Exam is in… | First gap | Then |
|---|---|---|
| 7 days | 1 day | Every 1–2 days |
| ~5 weeks | ~1 week | Every 1–2 weeks |
| ~10 weeks | 1–3 weeks | Every 2–3 weeks |
| 6+ months | 3–4 weeks | Monthly, plus a mixed review before mocks |
These come from the Cepeda (2008) pattern, where the best gap is a fraction of the time until the test. Treat them as starting points, not laws.
Adjust with a confidence score
After each review, rate the topic from 1 to 5:
- 1–2 (mostly forgot): review again in 1–2 days.
- 3 (got most of it, with effort): keep the schedule.
- 4–5 (easy and complete): double the next gap.
Want the tracker and the full schedule done for you? The Study System is my 66-page interactive PDF. It includes a fillable Spaced Repetition Tracker with the day 1, 3–4, 7–10 and 21 columns already set up, plus the error journal, a two-week plan and a protocol for each of eight techniques. 29 €, with a 14-day money-back guarantee. See what's inside The Study System →
Anki vs the paper version
You don't need an app to space your reviews. Both options work; choose the one you'll actually keep using.
| Anki (app) | Paper (Leitner box + tracker) | |
|---|---|---|
| Cost | Free on desktop, Android and web; paid on iOS | Index cards and a notebook |
| Best for | Atomic facts: vocabulary, definitions, formulas, dates | Facts and whole topics, essays, problem types |
| Scheduling | Automatic | You move cards between boxes and note dates |
| Risk | Review piles if you add too many cards | Forgetting to check the dates |
| Screen-free? | No | Yes |
Using Anki well
- Turn on FSRS (the modern scheduler in recent versions) and set desired retention to around 0.90. Lower it to 0.85 if reviews pile up.
- New cards per day: 10–20. Every new card creates future reviews; 20 new cards a day can mean 150+ reviews a day a month later.
- Do reviews before new cards, every day.
- One fact per card, and make the front a real question.
- Rate yourself honestly. Hesitated? That's Hard or Again, not Good.
Anki is brilliant for facts but not enough on its own for understanding. Combine it with written recall and past-paper questions.
The Leitner box (no app)
| Box | Review | Rule |
|---|---|---|
| 1 | Every day | New cards and anything you got wrong |
| 2 | Every 2 days | Right once |
| 3 | Every 4 days | Right twice in a row |
| 4 | Once a week | Right three times |
| 5 | Every 2 weeks | Nearly mastered; check before the exam |
Correct → the card moves one box to the right. Wrong → it goes back to Box 1, however far it had got.
For whole topics that don't fit on a card, use a simple tracker: list each topic, the date you first learned it, and tick off reviews on day 3–4, 7–10 and 21 with a 1–5 confidence score.
Protocol: the daily spacing routine
| Step | What you do | Time |
|---|---|---|
| 1 | Start every study day with reviews. Check your tracker or Anki; do what's due before anything new | 15–20 min |
| 2 | Make every review a recall. Blurt, answer questions or solve a problem. Never just re-read | — |
| 3 | Rate your confidence 1–5 next to the review | 1 min |
| 4 | Set the next date: 1–2 → in 1–2 days; 3 → keep schedule; 4–5 → double the gap | 1 min |
| 5 | Add today's new topic with its day 3–4 review date | 1 min |
| 6 | Once a week, mix. Combine three older topics in one recall or question set | 20 min |
If you get stuck: if a review comes out almost blank, don't push through for twenty minutes. Re-learn the topic with one quick recall loop and reset its schedule to day 1. That's the system working, not failing.
A real example: AP Chemistry, one topic over five weeks
- Mon 3 Mar: learns precipitation, acid–base and redox reactions in class; that evening, one 15-minute recall loop.
- Thu 6 Mar: blurts the three types; mixes up oxidation states in redox. Confidence 2, so next review Saturday.
- Sat 8 Mar: recall plus five practice questions. Redox holds. Confidence 3: next review in about a week.
- Sat 15 Mar: mixed set with the previous unit. Confidence 4: gap doubles to about three weeks.
- Sat 5 Apr: one released free-response question, timed. Full marks on the method. Confidence 5: monthly reviews until May.
Five short sessions, under two hours in total, did more than a weekend of cramming could have done.
Common mistakes
- "Spacing" by re-reading on a schedule. Each review must be a retrieval attempt. Timing alone isn't the magic; timed recall is.
- Reviewing too soon because forgetting feels bad. Some forgetting is the point. Aim for "got most of it, with effort".
- Adding too many new cards or topics. New material creates future reviews. Cap new Anki cards at 10–20 a day.
- Massing everything into the last week. Put each topic on your tracker the day you first learn it.
- Missing days, then quitting. After a missed day, do only the overdue reviews of your weakest items. Don't try to clear everything at once.
How spacing fits with the other techniques
Spacing tells you when to study. Active recall tells you how. Together they're the two high-utility techniques in the research ranking, and the backbone of the plan in how to study for exams. Parents: the most useful thing you can ask is "what's due for review tomorrow?" (more on the for parents page).
FAQ
What is spaced repetition in simple terms?
It's reviewing the same material several times with growing gaps in between (for example day 1, 3, 7 and 21), and testing yourself from memory at each review instead of re-reading.
What is the best spaced repetition schedule?
A good default is day 1, day 3–4, day 7–10, day 21, then every 4–6 weeks. If the exam is close, shorten the gaps; if a topic is easy, lengthen them. Use a 1–5 confidence score to adjust.
Is Anki necessary for spaced repetition?
No. Anki is excellent for facts, but a paper Leitner box and a simple topic tracker work just as well for many students, especially for whole topics, essays and problem types.
How many new Anki cards should I add per day?
Around 10–20. Every new card creates future reviews, and adding too many is the most common reason students give up on Anki.
Can spaced repetition work if my exam is in a week?
Yes, with shorter gaps: review each topic every 1–2 days, always by recalling it from memory. You'll remember more than by cramming the same hours into one or two days.
Why does spacing feel less effective than cramming?
Because reviews after a gap feel harder. That effort is what makes memory last. In one study, 90 % of students learned more with spacing, but 72 % believed cramming had worked better (Kornell, 2009).
About the author
Quino (ProfeQuino) has taught in Spanish secondary schools since 2016, mainly at Colegio Cristo Crucificado in Mula and before that at Colegio Sagrado Corazón in San Javier, working with students aged 12 to 18. He writes about evidence-based study methods and exam preparation at quino.pro. More about Quino →
Related: Active Recall · How to Study for Exams · Best Study Techniques Ranked · For Parents · The Study System (PDF)
References: Bjork (1994), in Metacognition: Knowing about knowing, MIT Press · Cepeda et al. (2006), Psychological Bulletin 132(3) · Cepeda et al. (2008), Psychological Science 19(11) · Donoghue & Hattie (2021), Frontiers in Education 6 · Dunlosky et al. (2013), Psychological Science in the Public Interest 14(1) · Kornell (2009), Applied Cognitive Psychology 23(9) · Murre & Dros (2015), PLOS ONE 10(7).