Spaced Repetition (SM-2) Schedule Calculator
Spaced repetition leverages the Ebbinghaus forgetting curve by lengthening each review interval after a successful recall, boosting long-term retention. Enter a study date and ease factor (default 2.5) to see the future review dates recommended by Piotr Wozniak's SM-2 algorithm.
Please enter a valid number
| # | Review date | Interval (days) | Day from study |
|---|
Formula
I₁ = 1 day I₂ = 6 days Iₙ (n ≥ 3) = round(Iₙ₋₁ × EF) (EF = ease factor; SM-2 floor 1.3, default 2.5)
- · SM-2 was published by Piotr Wozniak (SuperMemo, 1985–1990) and underpins modern spaced-repetition apps such as Anki, Mnemosyne and SuperMemo.
- · The default ease factor of 2.5 corresponds to a "passed easily" review. If you frequently forget the card, drop EF toward the SM-2 floor of 1.3 for tighter intervals.
- · This calculator assumes perfect recall every time (quality q = 5), so EF stays constant; real Anki/SuperMemo lowers EF whenever you fail a card.
- · The first two intervals (1 and 6 days) are fixed in SM-2 and do not depend on the ease factor.
- · Dates are computed as UTC calendar-day arithmetic, so daylight-saving transitions do not shift any review by a day.
Frequently asked
Why is the first review at 1 day and the second at 6 days?
Wozniak fixed these as SM-2 constants based on SuperMemo trials: the first recall the day after learning is optimal for consolidating short-term into long-term memory, while a follow-up roughly a week later anchors the long-term trace. Only from the third review onward does the interval grow by the ease factor.
What ease factor should I pick?
SM-2 defaults to 2.5, which suits most well-learned cards. Anki adjusts EF in real time: q = 5 adds 0.10, q = 4 keeps EF, and q ≤ 3 reduces it (floor 1.3). If you keep forgetting a card, drop to 2.0 or even 1.5; for very easy cards push up to 2.7–3.0. This tool keeps your chosen EF constant across the full projection.
Why does the schedule differ slightly from what Anki shows?
Anki layers a few tweaks on top of SM-2: an interval modifier (default 1.0, configurable 0.8–1.5), fuzz factor (random ±a few days), separate Hard/Good/Easy boosts, and a hard cap (default 100 years). If you stick to defaults and press Good every time, this tool will closely match Anki; pressing Easy or changing the modifier diverges the numbers.
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