What is spaced repetition?

What is the forgetting curve?

Memory fades in a predictable shape. In 1885 Hermann Ebbinghaus tested his own recall over time and plotted what we now call the forgetting curve: learn something today and, without review, you lose much of it within days, steeply at first and then more slowly. The curve is not a flaw to fix but a fact to work with. Each time you successfully recall something, the curve for that item flattens, so the memory decays more slowly than it did before. Spaced repetition exploits this by placing each review near the dip in the curve, the point where recalling does the most to strengthen the memory.

Why does spacing beat cramming?

Cramming feels efficient because everything is fresh and easy to recall in the moment. The catch is that ease at study time is a poor sign of memory later. The spacing effect, the finding that the same study spread over time beats the same study massed together, is one of the most reliable results in memory research. A large review by Cepeda, Pashler, Vul, Wixted and Rohrer in 2006 looked across many studies of distributed practice and found that spacing reliably improved long-term retention.

• Cramming loads short-term memory, and that fades fast once the test is over.
• Spacing forces effortful recall after partial forgetting, and that effort is what builds durable memory.
• Because the intervals grow, the total number of reviews stays small even across thousands of cards.

What does a spaced schedule look like?

Imagine you learn the German word Vergangenheit, meaning the past. You review it the next day and recall it with a little effort. The following review is set a few days out; you get it again, so the next gap is a week, then a couple of weeks, then a month, then several months. Each success buys a longer rest, because every clean recall is evidence the memory has grown more stable and can survive a longer wait. If one day you blank on it, the interval shrinks back to a day or two and starts climbing again from there. Over a year, a word you once saw daily might need only three or four reviews to stay solid, which is why a deck of a few hundred cards stays manageable even as your vocabulary keeps growing.

How do you actually do spaced repetition?

• Turn what you are learning into question-and-answer cards, with one idea per card.
• Review each card when it is due, not earlier and not much later.
• Recall the answer before you check it; the retrieval is what makes spacing work.
• Rate yourself honestly, because the schedule is only as good as the feedback you give it.
• Let an algorithm handle the timing so you can spend your attention on the material.

What are common mistakes with spaced repetition?

The method is simple, but a few habits quietly undo it. The most common is reviewing too early, out of eagerness or anxiety, before any forgetting has set in. A review when recall is still effortless teaches you little and wastes the slot; the value lives in the small struggle of near-forgetting. The second is adding new cards faster than you can sustain their reviews, so the daily queue swells until the habit collapses under its own weight. A steadier intake keeps the schedule survivable.

Two more are worth naming. Rating dishonestly, marking a card as known when you actually guessed, corrupts the schedule and pushes the card too far out, so be candid about what really happened. And skipping days lets reviews pile into a wall that feels impossible to face. If a backlog does build, clear the oldest cards first and accept a few lower ratings rather than abandoning the deck; the schedule is forgiving once you start feeding it again.

Where does the algorithm come in?

Picking intervals by hand is tedious and imprecise, and it gets worse as a deck grows. Modern tools use a scheduler to predict each card's forgetting point and place the review there automatically. Recense uses FSRS, the open-source Free Spaced Repetition Scheduler, which models each memory and aims each review at a recall target you can leave at its sensible default. You add cards and review what is due; the timing takes care of itself.

Bottom line: forgetting is predictable, so reviews should be scheduled, not guessed. Space them at growing intervals, recall before you check, and a few minutes a day will hold far more than hours of cramming ever could.