Free Spaced Repetition Calculator
Calculate optimal review intervals using spaced repetition principles. Determine when to review material for maximum long-term retention.
Days before first review
Multiplier for interval growth (2.5 is standard)
Which review iteration to calculate
Next Interval (days)
16
Total Days Since First Study25
Next Interval (weeks)2.3
Next Interval (days) vs Initial Interval (days)
How Spaced Repetition Works
Spaced repetition increases review intervals over time as material is learned.
Formula
Next Interval = Initial Interval x Ease Factor ^ (Review Number - 1)
The ease factor determines how quickly intervals grow. Standard is 2.5, meaning each interval is 2.5x the previous one.
Typical Schedule
Example Calculation
Starting with a 1-day interval and ease factor 2.5, calculating the 4th review.
- 01Next interval = round(1 x 2.5^3) = round(15.625) = 16 days
- 02Review 1: 1 day, Review 2: 2.5 days, Review 3: 6.25 days, Review 4: 15.6 days
- 03Total days elapsed ≈ round(1 x (2.5^4 - 1) / 1.5) = round(25.4) = 25 days