Cramming has one genuine strength: it gets you through tomorrow's test. Its weakness is just as real: a few weeks later, most of what you crammed has evaporated. That becomes expensive in cumulative fields such as medicine, pharmacy, engineering and languages, where third-year modules sit on first-year foundations.
Spaced repetition does not ask you to study more hours. It spreads the same hours across several sessions separated by growing gaps. The principle is easy; the hard part is keeping the review load from ballooning until you abandon the system three weeks in.
What the forgetting curve actually tells you
In the late nineteenth century Hermann Ebbinghaus experimented on himself with nonsense syllables and described what we now call the forgetting curve: retention falls quickly over the first hours and days, then levels off. The part people forget is more useful: each well-timed review makes the next curve flatter, so the gap before the following review can be longer.
The exact shape varies widely between people and between kinds of material. There is no universal percentage, so be sceptical of infographics claiming you forget a fixed share within twenty-four hours. The shape is reliable; the specific numbers are not.
Why spacing works
Reviewing immediately after learning does little, because the material is still warm and recall costs no effort. Reviewing after you have forgotten almost everything means relearning from scratch. The productive zone lies between: when you are about to forget but can still retrieve it with some effort. Spacing is simply a way of landing reviews in that zone.
This is why spaced repetition pairs naturally with retrieval practice. Spaced rereading beats massed rereading, but spaced self-testing is the combination that really pays.
A paper schedule: the five-box system
You do not need software. A card box with compartments, usually called a Leitner box, handles a few hundred cards comfortably:
| Box | Review when | If correct | If wrong |
|---|---|---|---|
| 1 | Every day | Move to box 2 | Stay in box 1 |
| 2 | Every other day | Move to box 3 | Back to box 1 |
| 3 | Twice a week | Move to box 4 | Back to box 1 |
| 4 | Once a week | Move to box 5 | Back to box 1 |
| 5 | Every two weeks | Retire it or review monthly | Back to box 1 |
“Wrong means back to box 1” sounds harsh, but it is exactly what makes hard cards come up more often than easy ones, putting your effort where you are weakest.
Setting up Anki sensibly
Apps such as Anki calculate intervals from how you grade each card. Common beginner mistakes:
- Adding too many new cards a day. Every new card today generates several reviews over the coming weeks. Adding a hundred in one day sets a trap for next week. Start with 10–20 new cards a day, watch your review count for two weeks, then adjust.
- Pressing “Easy” to make cards go away. They get pushed far out and you forget them. Honest grading is what makes the algorithm work.
- Downloading someone's deck of several thousand cards. Shared decks can help in fields with standard content, such as vocabulary or pharmacology, but cards you write from your own lectures are easier to remember and contain only what you need.
- Skipping a few days and facing hundreds of overdue cards. Do not try to clear them in one sitting. Pause new cards and spread the backlog over three or four days.
What belongs in a spaced repetition system
Spaced repetition shines for items that are discrete, need exact recall and will be used for a long time: vocabulary, terminology, formulas, drug doses, dates, symbols. It is weaker for long chains of reasoning or multi-step problem solving. For those, schedule spaced practice, such as re-doing a past paper a week later, rather than cramming it onto cards.
One rule keeps cards meaningful: each card asks one thing, answerable in a few seconds. If a card needs more than a minute of thought, it is an exercise, not a card.
Spacing without software: across a whole term
Spacing also works at the level of a module. A simple term plan:
- End of each class: ten minutes of blank-page recall on what was just covered.
- End of each week: thirty minutes of self-testing on that week's topics, marking wrong answers.
- End of each month: redo every wrong answer from the month, plus a short mixed quiz.
- Two weeks before the exam: a timed mixed paper, then targeted work on weak areas.
With this in place, the week before the exam becomes a week of fine-tuning rather than relearning from scratch.
A worked example: 600 terms in three months
Say you need 600 technical terms for an exam in about ninety days. Adding ten new terms a day gets everything into the system within sixty days, leaving thirty days purely for review. In the early weeks, daily reviews usually run to several times the number of new cards, so in practice you will review a few dozen cards a day, roughly 15–25 minutes. Compared with trying to learn 600 terms in the final fortnight, total time is similar, but what you still know after the exam is very different.
Things not to worry about
- Finding the perfect interval. Roughly sensible spacing captures most of the benefit; the differences between reasonable schedules are small.
- Reviewing at an exact time. Being a day or two late does not break the system.
- Keeping every card forever. Cards you know cold and no longer need can be deleted or suspended.
This week, pick one module with lots of exact-recall material, write fifteen cards from your latest lecture, and schedule reviews for tomorrow, three days out and one week out. After three weeks, count how many you can answer instantly. That number is the real measure.
Câu hỏi thường gặp
What is spaced repetition?
It is reviewing the same material several times with gradually increasing gaps, instead of in one sitting. Each review lands when you are close to forgetting, which strengthens memory more.
How many new Anki cards should I add per day?
Beginners do well with 10 to 20 new cards a day. Each new card creates several reviews in later weeks, so watch your review load for two weeks before increasing.
What should I do if I missed several days of Anki reviews?
Pause new cards and spread the backlog over a few days. Some cards will have lapsed and return to short intervals, which is normal.
What is a Leitner box?
A paper flashcard system with several compartments, each reviewed less often than the one before. Correct cards move forward a box; wrong cards go back to the first box.
Does spaced repetition work for maths?
Flashcards suit formulas and definitions, while problem-solving skill is better spaced by redoing problems after a week or a month. The spacing principle still applies; only the format changes.
