Next LessonWhat is spaced repetition, and how do you use it?
Spaced repetition is a way of reviewing that brings each fact back just before you would forget it. Each time you remember it, the gap before the next review grows: a day, then a few days, then weeks. Each time you miss it, the gap shrinks again. Your review time goes to the things you are about to lose, not the things you already know.
Written by Next Lesson, which schedules every review this way. You can also run it with paper cards and a calendar; the section on doing it by hand says how.
The short version
- Memory fades on a curve. Most of a new fact is gone within days unless you use it.
- Each successful recall slows the fade, so the next review can wait longer.
- Review when it is almost gone, not when it is still fresh and not after it is lost.
- Always review by answering, not by rereading: see active recall.
Why does spaced repetition work?
Forgetting is not a failure; it is what makes practice useful. Pulling a fact back when it has started to fade takes effort, and that effort is what strengthens the memory. Reviewing something you saw five minutes ago takes no effort and adds very little. Reviewing something you forgot a week ago means learning it again. The useful moment is in between, and spaced repetition is simply a way of finding it for every fact separately.
Is spaced repetition better than cramming?
For anything you need to keep, yes. Cramming can get you through a test the next morning, because the facts are still fresh. A week later most of it has gone. The same total study time spread over several sessions leaves far more behind. If your exam is weeks away, spacing wins; if it is tomorrow, cram and then space it out afterwards so the course still makes sense next term.
| Review | Gap before it |
|---|---|
| 1st | Same day, or the next day |
| 2nd | A few days |
| 3rd | About a week or two |
| 4th | A month or more |
Real schedules adjust the gaps for each fact and for how you answered, so these numbers are only the shape.
How do I do spaced repetition by hand?
Use three or four boxes of paper cards. New cards go in box one, which you review every day. A card you get right moves up a box; a card you miss goes back to box one. Review box two every few days, box three once a week, box four every few weeks. It works, but it takes discipline to keep and the cards have to be written first.
How does Next Lesson use spaced repetition?
Next Lesson builds the cards and questions from your lectures, PDFs and notes, so there is nothing to write by hand. It schedules reviews with FSRS, a modern spaced repetition method that estimates, for each item, how likely you are to remember it today. What you missed, and what is fading, comes back until it sticks. To get material in, see how to turn a lecture video into study notes or how to turn a PDF into flashcards.
Questions
What is spaced repetition in simple terms?
Reviewing each fact just before you would forget it. Each time you remember it, the next review comes later; each time you forget it, it comes back sooner.
How long should the gaps be?
Roughly a day, then a few days, then a week or two, then a month or more, growing each time you get it right. A good scheduler sets the gap for each fact separately, based on how you answered.
What is FSRS?
FSRS (Free Spaced Repetition Scheduler) is an open method for scheduling reviews. It estimates how likely you are to remember each item and brings it back when that chance drops. Next Lesson uses it for every review.
How many minutes a day does spaced repetition take?
For a normal course load, ten to twenty minutes a day is enough to keep up, because you only review what is due. Skipping days makes the pile bigger, so a little every day beats a lot once a week.