How Spaced Repetition Scheduling Works — the Algorithm Behind Fulin Flashcard

If you’ve used any flashcard app for more than a week, you’ve probably noticed the same frustration: half the deck is stuff you already know cold, and the other half is the handful of words you keep getting wrong — but the app treats them all the same, showing you the full deck every session.

Spaced repetition exists to fix exactly that.

The core idea

Every card has a “forgetting curve” — the more recently and more successfully you’ve recalled it, the longer you can wait before you need to see it again without forgetting it. Spaced repetition tracks that curve per card and schedules the next review right before you’d forget, not on a fixed daily cycle.

In practice this means:

• A card you’ve nailed five times in a row might not resurface for two or three weeks.
• A card you keep fumbling comes back tomorrow, or even later today.
• The deck naturally reorganizes itself around what you actually need to practice.

Why this matters more than deck size

A 500-card deck reviewed with spaced repetition is more efficient than a 50-card deck reviewed in a fixed loop, because most of a session’s time in a fixed-loop app is spent re-confirming things you already know. Spaced repetition spends that time budget on the cards that need it.

How Flashcard applies this

Flashcard tracks recall per card and adjusts each card’s next-review interval based on whether you got it right, and how confidently. Cards are organized into topic decks, so you can keep separate decks for grammar, vocabulary, or a specific unit of study — but the underlying scheduling logic is the same across all of them: show the card right before you’d forget it, not on a calendar.

If you’re building your own deck, the practical upshot is simple: don’t worry about deck size or trying to review “the whole thing” every day. Add cards as you encounter new material, and trust the schedule to surface what needs attention.

Try it at flashcard.fulinlabs.com, or read more about the project on its hub page.