Spaced repetition, explained simply

Memory fades in a predictable way. Right after you learn something you can recall it easily, and a few days later most of it is gone. Every time you successfully recall a fact just as it is starting to slip, the memory gets harder to lose. That is the whole mechanism: recall at the right moment, not more time with the book.

Two things matter. First, you have to retrieve, not review. Reading the answer is passive; answering before you look is the part that works. Second, the gap between reviews should grow. A card you got right three times does not need to come back tomorrow.

You do not need a complicated system. For most subjects this is enough:

• Same day you learn it, once.
• Next day.
• Three days later.
• A week later.
• Two to three weeks later.

If you miss a card, drop it back to the start of the sequence. If a card is easy three times running, stretch the gap or retire it. The point is that hard material comes back often and easy material stops eating your time.

Spaced repetition feels harder because it is harder. Rereading gives you a smooth, confident session and very little retention. Retrieval gives you a session full of small failures and much better retention. Do not judge a study method by how comfortable it feels while you are doing it. Judge it by what you can recall three days later, cold.

Turn your material into a quiz deck so every card forces an answer before showing one. Run the deck the same evening, then again the next day. Your score history tells you which sessions went badly, which is your signal to review sooner.

For a longer subject, group the decks into a learning path with a deadline. The path view shows the last time you opened each deck, which is the fastest way to spot the one you have been avoiding for two weeks.

Related: how to make good flashcards and turning a PDF into a deck.

• Cramming everything into one long session the night before.
• Reviewing cards you already know because they feel good to answer.
• Making cards so long that a review takes a minute each.
• Starting a new deck every week and never returning to the old ones.

Fifteen focused minutes a day, spread across two or three decks, beats a three-hour session on Sunday. The schedule is the method.