Skip to content

Spaced repetition

Spaced repetition is a study method in which you review information at increasing intervals. Each successful review makes the memory more durable, so the next one can wait longer.

100%50%0%Day 013714
Estimated retention without review (grey) and with reviews on days 1, 3 and 7 (blue). Illustrative shapes, not measured values.

Why does it work?

Memory fades along a forgetting curve. Each successful recall makes the next decline slower, so reviews can be spaced further apart.

The forgetting curve

Which algorithm decides when?

Most apps use SM-2, from 1987, or the newer FSRS, which estimates how likely you are to recall each card and schedules it when that likelihood falls to a target.

Compare the algorithms

Which app should you use?

Anki is the free reference for power users. Simpler apps trade some control for less setup.

Spaced repetition apps

Contents

Learn

The science of memory and study

All of Learn

Algorithms

SM-2, FSRS and Leitner

All algorithms

Apps

Profiles of flashcard apps

All apps

How spaced repetition works

Memory fades along a forgetting curve, first measured by Hermann Ebbinghaus in 1885. Each successful review makes that curve flatter, so the next review can wait longer than the one before: a day, then a few days, then weeks and months.

Spaced study beats cramming for long-term retention, a finding known as the spacing effect. A flashcard app tracks every card and schedules its next review with an algorithm such as SM-2 or FSRS. The method suits anything you must recall on demand: vocabulary, medicine, law, definitions.

Apps

Each app profile covers the same questions: price, platforms, scheduling and the cards you can make, checked against official sources.

  • Anki

    The free, open-source reference, with deep control over cards and scheduling.

  • Recall

    A simple web app built on FSRS, with AI and connectors for Claude and ChatGPT.

  • Quizlet

    A popular study app with shared sets and games, and spaced repetition on the web since 2026.

  • RemNote

    A note-taking app with flashcards built into your notes, scheduled with SM-2 or FSRS.

  • SuperMemo

    The original spaced repetition software, with advanced algorithms on Windows and language courses on mobile.

  • Knowt

    A free study app in the style of Quizlet, with AI tools and a spaced repetition mode.