Recall Interval Calculator

This calculator can use three approaches: an SM-2 style rule, a forgetting-curve rule, or an exam-aware hybrid.

• SM-2 easiness update: EF' = EF + (0.1 − (5−q)×(0.08 + (5−q)×0.02)), clamped to 1.3–3.0.
• SM-2 interval: I = 1 (first), 6 (second), else I = round(previous × EF').
• Retention scaling: I' = round(I × ln(1/r) / ln(1/0.85)), clamped for stability.
• Forgetting curve: p = e^(−t/s) ⇒ t = −s ln(p), then adjusted for difficulty and quality.
• Hybrid compression: If the exam is near, cap I' to keep room for more reviews.

1. Enter your topic, last review date, and exam date.
2. Set difficulty and recall quality from your latest session.
3. Pick a retention level; 80–90% works well for tests.
4. Choose an algorithm; Hybrid is best for fixed deadlines.
5. Adjust study days and buffer days, then calculate.
6. Download CSV or PDF and follow the listed dates.

1) What is a recall interval?

A recall interval is the time gap between review sessions for the same material. The goal is to review right before forgetting, which improves long-term memory efficiency.

2) Which algorithm should I choose?

Use Hybrid when you have a fixed exam date. Use SM-2 style for ongoing decks without deadlines. Use Forgetting curve when you prefer probability-based timing over step rules.

3) How do I rate recall quality?

Use 5 for perfect recall, 3 for partial recall with effort, and 0 when you forgot. Your rating influences how much the interval grows or shrinks.

4) What does desired retention mean?

It is the minimum recall probability you want before a review. Higher targets create more frequent reviews. Lower targets create wider spacing and may risk more forgetting.

5) Why add buffer days before the exam?

Buffer days reduce burnout and leave room for light revision, practice tests, and sleep. They also prevent scheduling a heavy review session right before the exam.

6) What if I miss a scheduled review?

Update the last review date to the day you actually studied, keep difficulty and quality realistic, then recalculate. The schedule will shift to match your new timeline.

7) Why are some dates moved to the next day?

If you restrict study days, the calculator pushes reviews forward to the next allowed day. This keeps the plan practical instead of placing reviews on blocked days.

8) Can I use this for multiple subjects?

Yes. Run one schedule per subject or deck and export each file. For many topics, consider shorter max reviews and consistent study days to avoid overload.