Study Calculators
Spaced repetition schedule.
Enter the day you first learn a card and how well you recalled it at each review. The tool applies the published SM-2 steps and lists the next review dates. Runs in your browser; nothing is sent or stored.
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Review schedule
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Quick answer
In SM-2 the first review is 1 day after you learn a card, the second is 6 days after that, and each later gap is the previous gap times the ease factor (2.5 to start), rounded up. With ratings of 4 the gaps are 1, 6, 15, 38 and 95 days.
Worked example
Learn a card on 1 October 2026 and rate every review 4 (correct after a hesitation), which leaves the ease factor at 2.5. Gaps: 1, 6, 15 (6 x 2.5), 38 (15 x 2.5 = 37.5, rounded up) and 95 (38 x 2.5 = 95). Review dates: 2 Oct, 8 Oct, 23 Oct, 30 Nov 2026 and 5 Mar 2027, which is day 1, 7, 22, 60 and 155.
How it works
Steps from Piotr Wozniak's SM-2 description: the first gap is 1 day, the second is 6 days, and for n greater than 2 the gap is I(n-1) x EF, rounded up to a whole day. EF starts at 2.5. After each review the ease factor changes to EF + (0.1 - (5 - q) x (0.08 + (5 - q) x 0.02)), where q is your 0 to 5 rating, and is never allowed below 1.3. A rating of 4 leaves EF unchanged. A rating below 3 restarts the gaps from the beginning without changing EF.
This tool's choices. It rounds each gap up and uses that whole-day gap as I(n-1) for the next one. It applies the ease factor as updated by the earlier ratings. The source also tells you to repeat any card rated below 4 again in the same session until it scores at least 4; that same-day repeat is not scheduled here. The last row is the next review after the ratings you entered.
Sources (each page opened 2026-10-08):
- SuperMemo 2: Algorithm, Piotr Wozniak, 1990 (super-memory.com): the SM-2 steps, the ease-factor formula, the 2.5 start, the 1.3 floor and the rating scale
FAQ
What is the SM-2 algorithm?
SM-2 is the spaced repetition algorithm Piotr Wozniak described in 1990 for SuperMemo. It sets the gap before each review from your recall rating, so easy cards come back less often.
What are the SM-2 review intervals?
The first gap is 1 day, the second is 6 days, and each later gap is the previous gap times the ease factor, rounded up. At the starting ease factor of 2.5 that gives 1, 6, 15, 38, 95 days.
What happens when I forget a card?
A rating below 3 restarts the gaps from 1 day and 6 days. The ease factor is left unchanged by that review.
What is the ease factor?
A number that scales the gap between reviews. It starts at 2.5, moves with your ratings and cannot fall below 1.3.
Will this match Anki?
Not exactly. Anki and later SuperMemo versions use modified schedulers. This tool follows the original SM-2 text only.