How spaced repetition works

Spaced repetition means reviewing something at growing intervals: the next day, then a few days later, then weeks, then months. Each time you remember it, the gap before the next review gets longer. It’s how Anki, Flashfriend and most other flashcard apps decide what to show you each day.

The forgetting curve

A new word starts fading from memory almost as soon as you learn it. Hermann Ebbinghaus measured this on himself in the 1880s, and a modern replication found the same curve: steep forgetting in the first hours and days, then a long, slow tail (Murre & Dros, 2015).

Each review resets the curve, and the curve gets flatter every time. So the gaps between reviews can keep growing, and a word you’ve reviewed six or seven times can stay with you for months.

What the research says

Two findings do most of the work, and both have held up in decades of experiments:

• Spacing. Reviews spread out over time beat the same number of reviews crammed together. A review of 839 results from 317 experiments found the effect again and again, and found that the best gap grows with how long you want to remember (Cepeda et al., 2006).
• Testing yourself. Trying to recall a word, before you see the answer, fixes it in memory far better than rereading it (Roediger & Karpicke, 2006). Every flashcard review is a small test, which is half of why flashcards work.

How much total spacing you get matters more than the exact pattern. Growing gaps weren’t reliably better than equal ones in a direct test (Karpicke & Bauernschmidt, 2011). In practice, keeping up with your reviews is the most important part.

How often to review flashcards

• Every day, if you can. Spaced repetition works by catching each word on the day it’s due. A day off is fine; a week off leaves a pile.
• Keep new words steady. Each new word brings reviews with it for weeks. Ten new words a day is a good start. If reviews feel light after a few days, add more; if they pile up, add fewer.
• Answer honestly. If you didn’t remember it, say so. The schedule is only as good as your answers.
• Pick how much you want to remember. Apps that use FSRS let you set a target, like remembering 90 percent of your cards when they come up. Higher means more reviews; lower means fewer reviews and more forgetting.

Making each review count

Spaced repetition decides when you see a word. How well the word sticks between reviews depends on how you learned it. A word tied to a picture that means something to you, with a memory hook for its sound, is easier to recall when it comes up. See memory hooks and flashcards with pictures.

How Flashfriend does it

Flashfriend schedules every card with FSRS, the same algorithm Anki offers, with its default settings. You choose how much you want to remember and how many new words a day, and the rest is automatic. You’re tested both ways round, from the word to its meaning and from the meaning to the word, on your phone or computer, kept in sync. Sentence cards and grammar points follow the same schedule once they start.

If you’re coming from Anki, your review history comes with you: bring your Anki deck. See all the memory techniques behind every card.