Spaced repetition

• Review at longer and longer gaps instead of all at once.
• Each review comes when the memory has started to fade, so recalling it takes effort.
• It is the opposite of cramming.

Spaced repetition is a way of scheduling review. Instead of going over a fact many times in one sitting, you see it again after a gap, and then again after a longer gap. The gaps grow as the fact becomes familiar. This builds on the spacing effect: material reviewed over several days is remembered better than the same amount of review packed into one session.

Example: one flashcard over a week

Say you make a flashcard with the question "What does the mitochondrion do?" and the answer "It releases usable energy for the cell." You learn it today, which we will call day 0. A simple schedule has you review it on day 1, day 3 and day 7.

Each review comes at the moment the memory has started to slip, so you have to work a little to recall it. That effort is what strengthens the memory. If you could not recall the answer on a given day, you bring the next review closer; if it came easily, you can push it further out.

Check the gaps: 1 − 0 = 1 day, 3 − 1 = 2 days, 7 − 3 = 4 days. The gap doubles each time, which is a common pattern and not the only possible one.

Why it matters

Cramming feels productive because the material is fresh in your head, but that freshness fades quickly. Spaced review spends the same minutes in a way that keeps the memory going for longer. The total time can be small: a card that is easy takes a few seconds per review.

It pairs well with retrieval practice, because each review is an attempt to recall. To see it applied to a real deadline, read the guide on a spaced repetition plan for a test in three weeks.