The idea in one sentence
Memory fades on a curve, and a well-timed review resets that curve higher than before — so the next review can wait even longer. Spacing your reviews out, rather than repeating something many times in one sitting, is what moves material into long-term memory.
Why spacing beats cramming
Cramming packs many repetitions into a short window. It feels productive because the material is easy to recall in the moment — but that fluency is temporary, and most of it is gone within days.
Spreading the same number of repetitions over days and weeks feels harder, because each time you return the memory has faded a little and you have to work to retrieve it. That effort is exactly what makes the memory durable. Researchers call this the spacing effect, and it has been confirmed across hundreds of studies (see our sources page).
How to actually do it
You can run spaced repetition by hand with paper cards and a box, scheduling each card forward as you get it right. But tracking dozens or hundreds of cards quickly becomes a chore — which is why most people use software that schedules every review automatically.
In Koydo, you never set intervals yourself: the app brings each card back at the right moment, so you just study what comes up each day. If you want to see the schedule a spaced system produces, try our free spaced repetition calculator.
