> ## Documentation Index
> Fetch the complete documentation index at: https://mintlify.com/crizmo/KAnki/llms.txt
> Use this file to discover all available pages before exploring further.

# Spaced repetition

> Learn how KAnki's spaced repetition algorithm optimizes your learning schedule

KAnki uses a simplified SM-2 (SuperMemo 2) spaced repetition algorithm to help you learn vocabulary efficiently. Cards are scheduled for review at increasing intervals based on how well you remember them.

## How it works

When you review a card, KAnki calculates the next review time based on your response. Each card tracks:

* **Difficulty level**: Increases when you answer correctly, resets when you answer incorrectly
* **Next review date**: When the card will appear again in your study queue
* **Review history**: All your past answers with timestamps

## Review intervals

KAnki offers four response options when you reveal a card's answer:

<CardGroup cols={2}>
  <Card title="Again" icon="rotate-left">
    10 minutes - Resets the card's difficulty level
  </Card>

  <Card title="Hard" icon="clock">
    1 day - Keeps the same difficulty level
  </Card>

  <Card title="Good" icon="check">
    3 days - Increases difficulty by 1 level
  </Card>

  <Card title="Easy" icon="star">
    4 days - Increases difficulty by 2 levels
  </Card>
</CardGroup>

<Note>
  The intervals shown are base intervals. As your difficulty level increases, KAnki automatically extends these intervals using a multiplier formula: `interval × (1 + difficulty × 0.5)`
</Note>

## Difficulty progression

As you master cards, the intervals grow exponentially based on your difficulty level:

| Difficulty Level | Base Interval |
| ---------------- | ------------- |
| 1                | 1 day         |
| 2                | 3 days        |
| 3                | 1 week        |
| 4                | 2 weeks       |
| 5                | 1 month       |
| 6+               | 2 months      |

<Tip>
  Cards appear in your study queue when their `nextReview` timestamp is less than or equal to the current time. This means you'll only see cards that are actually due for review.
</Tip>

## Card data structure

Each card in KAnki stores the following information in main.js:217:

```javascript theme={null}
{
  front: "target language text",
  back: "translation",
  notes: "additional context",
  level: "N5",
  difficulty: 0,
  nextReview: timestamp,
  history: [{date: timestamp, result: true/false}],
  starred: false,
  timesViewed: 0,
  lastViewed: timestamp
}
```

## Incorrect answers

When you mark a card as "Again" or answer incorrectly:

1. The card's difficulty decreases by 1 (minimum 0)
2. The next review is scheduled for 10 minutes from now
3. The card is added to the error review queue
4. After completing your regular session, you'll be prompted to review incorrect cards

<Info>
  This immediate review system helps reinforce difficult vocabulary before they're forgotten.
</Info>

## Progress persistence

All spaced repetition data is automatically saved to your Kindle's localStorage at:

```
/Kindle/.active_content_sandbox/kanki/resource/LocalStorage/file__0.localstorage
```

You can reset your progress using the **Reset Progress** button in the app menu, which clears all review history while keeping your deck intact.