How spaced repetition works

You learn a new word on Monday. By Wednesday it’s gone. That’s normal: memory fades quickly at first, then more slowly. This is the forgetting curve, first described by Hermann Ebbinghaus in the 1880s.

The idea

Every time you successfully recall something, the memory gets stronger and fades more slowly. So the best moment to review a word is just before you’d forget it. Review too early and you waste time; too late and you’re learning it from scratch again.

Spaced repetition does this scheduling for you:

• A new card comes back after a short gap, perhaps a day.
• If you remember it, the next gap is longer: a few days, then a week, then a month.
• If you forget it, the gap shrinks again.

Over time, the words you know well barely take any of your time, and your reviews focus on the ones you’re still learning.

Rating your answers

After each card, you say how it went:

Button	Meaning	What happens
Again	I forgot it	It comes back soon
Hard	I got it, with effort	A slightly longer gap
Good	I got it	A normal, growing gap
Easy	Instantly	A much longer gap

Be honest: the schedule only works if the ratings reflect what you really remembered.

Making it work for Japanese

• Use words from things you watched. A card for 静か (shizuka, quiet) that reminds you of the late-night convenience store you saw it in is far easier to remember than a card from a list.
• Keep the sentence. Seeing a word in its original sentence helps with grammar and nuance too.
• A little, every day. Ten minutes daily beats an hour once a week. Streaks help.

In HitaruJP, tapping a word in a transcript lets you turn it into a flashcard with its sentence, and the review screen schedules it for you. On mobile, you can also import existing Anki decks.