Spaced repetition, explained
By the Braintoll team · · 3 min read
The short answer
Spaced repetition is a study method that schedules each review just before you would forget, with gaps that grow every time you remember: a day, then about a week, then weeks and months. After each card you rate how well you recalled it (Again, Hard, Good or Easy), and the schedule sets the next review. It beats cramming because recalling something right at the edge of forgetting makes the memory last much longer.
On this page
You learn a new word on Monday. By next Monday, it’s gone. That isn’t a bad memory — it’s a normal one. Spaced repetition is a way of studying that works with how forgetting happens instead of against it.
The forgetting curve
In the 1880s, the psychologist Hermann Ebbinghaus measured how quickly he forgot lists of nonsense syllables. The result became known as the forgetting curve: memory fades fast at first, then more slowly.
The useful part is what happens when you review. Every time you successfully recall something, the curve flattens — you forget it more slowly than before. So each review buys you more time until the next one is needed.
Review just before you forget
That leads to the core idea: instead of reviewing something twenty times in one evening, review it a few times with growing gaps in between — after a day, then about a week, then a few weeks, then months.
Each review is timed for the point where recall takes a little effort but still works. Pulling an answer out of memory strengthens it far more than re-reading it, an effect researchers call retrieval practice or the testing effect. Cramming feels productive, but spacing is what sticks.
How your rating sets the next review
You don’t calculate the gaps yourself. After revealing the answer, you rate how well you remembered it, and the schedule adjusts:
- Again — you forgot. The card comes back right away and its schedule starts over.
- Hard — you got there, but it was a struggle. The next gap grows, and future gaps for this card grow a little more slowly.
- Good — you remembered it. The next gap grows at the card’s usual pace.
- Easy — it was instant. The next gap grows, and future gaps for this card grow faster.
Braintoll uses the classic SM-2 algorithm: a card you remember comes back after one day, then after six, and from then on each gap is multiplied by that card’s ease factor. Easy ratings raise the ease factor, Hard and Again lower it. Cards you know well fade into the background; cards you struggle with stay in rotation.
Tips for cards that work
- One fact per card. “Capital of Australia” beats “Capitals of Oceania”.
- Ask, don’t show. Phrase the front as a question you have to answer, not a fact you just read.
- Keep answers short. If an answer needs a paragraph, split it into several cards. More rules with examples are in how to make flashcards.
- Rate honestly. Marking a shaky answer Easy only pushes the card out of reach right before you’d need it.
- Little and often. Five minutes a day beats an hour on Sunday.
- Before an exam, put the reviews in your plan. Learn a topic, review it the next day, about a week later and once more in the final week. Our guide on how to make a study plan shows how, with a free template.
The hard part: actually reviewing
The algorithm only works if you show up — and that’s where most people drop off. Reviews pile up, and a long backlog is easy to put off.
Braintoll ties your reviews to something you already do dozens of times a day: opening your most distracting apps. When you open one, a card from your library appears first. Every rating feeds the schedule, and once you’ve marked enough cards Easy, the app opens. Your reviews happen in small pieces throughout the day without you ever having to sit down to study.