Flashcard Spaced Repetition Scheduler

The Flashcard Spaced Repetition Scheduler applies the SM-2 algorithm — the scheduling method behind Anki and SuperMemo — to tell you exactly when to review each flashcard next. You grade how well you recalled a card, and the tool computes the new interval, ease factor, repetition count, and next review date. It also draws an animated forgetting curve and a projected review timeline so you can see how spacing your reviews keeps a memory alive with less total study.

What Is Spaced Repetition?

Spaced repetition is a learning technique that schedules reviews at increasing intervals — a day, then a few days, then weeks, then months. Each successful review strengthens the memory and lets the next gap grow. By reviewing a card just as you are about to forget it, you get the maximum memory benefit from the minimum number of repetitions. It is one of the most evidence-backed study methods for vocabulary, medical facts, formulas, and any material that must be recalled long-term.

The SM-2 Algorithm

SM-2 was designed by Piotr Woźniak in 1987 for SuperMemo. After each review you rate your recall quality from 0 to 5. The algorithm tracks three values per card: the repetition count (how many times in a row you have recalled it), the ease factor (how fast its intervals grow), and the current interval in days.

Here \(q\) is your recall quality and \(EF\) starts at 2.5 for a new card. The ease factor never drops below 1.3. If you grade a card below 3, the recall is treated as a failure: the repetition count resets to 0 and the card returns in 1 day.

The Recall Quality Scale

Grades 3, 4, and 5 are passes that extend the interval; grades 0, 1, and 2 are lapses that reset the card. Anki collapses these six grades into four buttons, mapping Again to grades 0–2, Hard to 3, Good to 4, and Easy to 5.

The Forgetting Curve

Hermann Ebbinghaus discovered that memory of new material decays roughly exponentially: without review you lose much of what you learned within days. Spaced repetition fights this by timing each review for the moment recall starts to drop. Every review resets retention to full strength, and because the memory is now more durable, the next decay is slower. That produces the widening saw-tooth pattern this tool draws — short gaps at first, then ever-longer ones as the card matures.

How to Use This Calculator

1. Grade your recall: Pick how well you remembered the card on the 0–5 scale, from complete blackout to perfect instant recall.
2. Enter the card state: Set the current repetition count, ease factor, and previous interval. For a brand-new card, leave the defaults (0 repetitions, ease 2.5, interval 0).
3. Set the review date: Optionally enter the date you reviewed the card. It defaults to today.
4. Click Calculate: See your new interval, ease factor, repetition count, and next review date, plus the forgetting curve and a projected schedule for the next six reviews.

Why Spaced Repetition Works

Frequently Asked Questions

What is the SM-2 spaced repetition algorithm?

SM-2 is the scheduling algorithm created by Piotr Woźniak for SuperMemo and later adopted by Anki and many other flashcard apps. After each review you grade how well you recalled the card on a 0–5 scale. SM-2 then expands or resets the interval until the next review and adjusts an ease factor that controls how quickly future intervals grow, so cards you know well come back less often and cards you struggle with come back sooner.

What is the ease factor?

The ease factor is a multiplier, starting at 2.5 for a new card, that determines how much the interval grows after each successful review. Easy recalls raise it, so intervals stretch faster, while hard recalls lower it, with a minimum of 1.3. An ease factor of 2.5 means a mature card's next interval is about 2.5 times the previous one.

How is the next interval calculated?

For the first successful review the interval is 1 day, for the second it is 6 days, and from the third onward it is the previous interval multiplied by the ease factor, rounded to whole days. If you fail a card (grade below 3) the repetition count resets to zero and the card is scheduled again in 1 day.

What is the forgetting curve?

The forgetting curve, first described by Hermann Ebbinghaus, shows how memory of new information fades over time. Spaced repetition works by scheduling each review just as recall begins to drop, which resets the curve to full strength and makes the next decay slower. The result is the saw-tooth pattern shown by this tool, where review intervals get longer as the memory strengthens.

Is this the same scheduling Anki uses?

This tool implements the classic SM-2 algorithm, which is the basis of Anki's traditional scheduler. Modern Anki also offers FSRS, a newer algorithm, and adds extras such as learning steps, fuzz, and interval modifiers. The core interval and ease-factor behavior shown here matches SM-2, so the numbers are representative of a standard spaced repetition schedule.

What grade should I give a card?

Use 5 for instant confident recall, 4 for a correct answer after a brief hesitation, and 3 for a correct answer you only reached with serious effort. Grades 0 to 2 mean you failed to recall the card: 2 if the answer felt easy once you saw it, 1 if it felt familiar, and 0 for a complete blackout. Any grade below 3 resets the card.

Additional Resources

• Spaced Repetition - Wikipedia
• Forgetting Curve - Wikipedia