The spaced repetition schedule that works for most material: review 1 day after learning, then 3 days, then 7, then 14, then 30. Each review is a short self-quiz, not a reread. Five sessions and most facts are locked in for months. The gaps roughly double because every successful recall flattens your forgetting curve. Students who space reviews this way remember 2 to 3 times more than students who cram the same hours in one sitting (Cepeda et al., 2006).
Do the exact intervals matter?
Not much. The 1-3-7-14-30 pattern is an approximation, not a law. What matters is that the gaps exist and keep widening. The real optimal interval depends on how hard the material is for you, how well you learned it the first time, and how much you already know about the topic. A vocabulary word in a brand new language needs tighter gaps than a concept that hooks onto something you already understand.
Apps like Anki and Lexie use algorithms (SM-2, FSRS) that adjust the intervals per question. Shorter when you keep missing something, longer when recall is easy. The fixed schedule below is a fine starting point if you are doing this by hand.
Review
When?
Why?
1st
1 day after learning
Catches the steepest part of the forgetting curve
2nd
3 days after 1st review
Memory is fading but still retrievable
3rd
7 days after 2nd review
Tests whether it's moving to long-term storage
4th
14 days after 3rd review
Spaced far enough that recall takes real effort
5th
30 days after 4th review
If you remember it now, you'll remember it for months
Can you use spaced repetition when you only have 3 days?
Spaced repetition was built for weeks of slow review. If your exam is in three days you can still use the principle. Spread the sessions out and test yourself instead of rereading.
Day 1
Learn the material actively. Don't just read it. Make questions, cover your notes and try to recall the key bits, write down what you remember without peeking. Notice what you don't actually know yet.
Day 2
Go back through everything from Day 1, starting with what you got wrong. The 24-hour gap means some of it slipped. That's the point. Pulling it back out of your brain when it's gone fuzzy makes the memory stick harder than if you'd kept staring at it.
Day 3
One more pass. Focus on the stuff that tripped you up yesterday. Don't pull an all-nighter. Sleep is when your brain files everything. A focused 45 minutes will beat a four-hour zombie session.
You won't retain this the way you would with a 30-day schedule. Most of it leaks out within a week. But for tomorrow's exam, spaced sessions plus active recall blow a single cram session out of the water.
Why do the gaps keep doubling?
Spaced repetition fights your instincts. Your brain wants to study whatever feels least familiar, which usually means cramming the night before. Cramming works for tomorrow's test and fails for next month's final.
The forgetting curve, which Hermann Ebbinghaus mapped out in 1885 and modern research keeps confirming, says you lose around 70% of what you learn within 24 hours if you don't review it. The useful bit: every time you successfully pull something back out of your head right at the edge of forgetting, the curve flattens. The interval before you forget doubles or triples.
So a concept reviewed at 1 day, 3 days, 7 days, and 21 days is basically permanent. Four short sessions. Cramming the same thing four times in one night gives you a fraction of that.
How do you keep the schedule going?
You need a way to track intervals. That's either an app (Anki, Lexie, RemNote) or something manual.
The manual version is the Leitner box method. Five boxes, folders, or piles. New material starts in Box 1, which you review every day. Get it right, it moves to Box 2 (every three days). Right again, Box 3 (weekly). And so on. Get it wrong at any level and it drops back to Box 1.
With an app, the algorithm does the scheduling. Your only job is to show up and do the reviews. The one rule that matters: do them every day, even if the pile is tiny. Skipping a day starts a backlog and backlogs grow fast.
What to space: factual stuff like vocabulary, dates, formulas, definitions. Flashcards are the classic format for a reason, they're built for exactly this. Problem-solving works too, you just space out the problem types instead of drilling them all in one sitting.
Pair the spacing with active recall every time. Try to answer before flipping the card. The schedule tells you when to review. Active recall is how you do it.
Frequently asked questions
Three different ways to automate the schedule. Leitner is the simplest. Physical or digital boxes, correct cards move forward, wrong ones go back to box one. It works but the intervals don't bend. SM-2 came out of Piotr Wozniak's work in 1987 and was Anki's default for years. It adjusts intervals based on a difficulty rating you give each card. FSRS (Free Spaced Repetition Scheduler) is newer and more accurate. It models your memory mathematically instead of relying on fixed rules, so it gets closer to predicting the moment you're about to forget. Anki (since v23.10) and Lexie both use FSRS by default. For most students the algorithm matters less than showing up. A mediocre algorithm used daily will outperform a perfect one abandoned after a week.
For long-term retention, by a lot. Cramming can carry you through tomorrow's test. The scores on an immediate exam might look similar. But a week later, crammers have lost 70 to 80% while spaced learners have kept 70 to 80%. For cumulative exams, professional certifications, or anything where you need the knowledge past next Tuesday, spaced repetition wins easily. Total study time tends to be lower too, since you're not relearning the same material from zero.
For a normal course load, 15 to 30 minutes of reviews a day. Consistency matters more than duration. 15 minutes a day will beat one three-hour session a week. If your daily review is creeping past 45 minutes, you're adding new cards faster than you can sustain. Throttle the new additions. 10 to 20 new items a day works for most students.
Yes, you just have to change the format. Skip the simple Q&A flashcards and write prompts that need a paragraph. Something like "Explain the causes of World War I in 3 to 4 sentences" or "Outline the arguments for and against utilitarianism." You're not writing a full essay every time. You're rehearsing the key arguments, evidence, and structures so that on exam day you can build the essay out of pieces you already know cold, instead of trying to invent everything under pressure.
Four big ones. Reviewing cards you already know well, which adds time but not memory. Spacing out rereading instead of self-testing, which loses most of the benefit. Quitting the schedule because reviewing old material feels wrong when new material is piling up. And adding 200 cards on day one, which makes next week's review pile a nightmare. Add 10 to 20 a day and trust the intervals.
