Spaced Repetition Scheduler
Schedule review dates using the SM-2 algorithm, showing how the interval and ease factor change with each recall grade and how the workload settles over time.
Last reviewed by the Radiatus Cloud team
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Forgetting is predictable, so reviewing can be scheduled
Memory for something learned once decays rapidly at first and then more slowly, and each successful recall flattens the curve. Reviewing just before the point of forgetting is far more efficient than reviewing on a fixed schedule, because an easy item wastes effort when reviewed too soon and a hard one is lost when reviewed too late. Spaced repetition schedules each item individually according to how well it has been recalled.
SM-2 is simple and still the basis of most systems
The algorithm published in 1987 tracks two numbers per item: the current interval and an ease factor. A successful recall multiplies the interval by the ease factor, and the grade adjusts the ease factor slightly up or down. A failure resets the interval to one day while keeping most of the accumulated ease. Modern systems have improved on it, and the structure of interval times ease with a reset on failure remains the core of nearly all of them.
The workload is the part people underestimate
Adding twenty new items a day produces a review load that grows for weeks before settling, because each item generates reviews at expanding intervals. The steady state is roughly the daily new items divided by the average interval growth, and it arrives long after the enthusiasm that set the rate. Modelling the load before committing to a rate is what stops a deck being abandoned.
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Frequently Asked Questions
What do the grades mean?
They record how the recall went, from a complete blackout to instant and effortless. The grade determines whether the interval grows and by how much the ease factor is adjusted, so grading honestly matters more than grading generously.
What is the ease factor?
A per-item multiplier for the interval, starting at 2.5. Easy items drift upwards and hard ones downwards, so the schedule adapts to each item rather than applying one rule to everything.
Why does a failure reset the interval?
Because a forgotten item has to be relearned, and the evidence that it was known for a long interval no longer holds. The ease factor drops but does not reset, so an item that was previously easy recovers faster than a new one.
How many new items a day can I sustain?
Fewer than most people start with. Each new item generates a stream of reviews at expanding intervals, so the daily load keeps growing for weeks before settling. Twenty new items a day typically settles at a few hundred reviews a day.
Is SM-2 still the best algorithm?
It is no longer state of the art. Newer schedulers model forgetting more accurately and adapt faster. SM-2 remains a reasonable default, is simple enough to understand fully, and the difference matters less than reviewing consistently.
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How to Use
Enter your recall grades to see when each review falls due.
Disclaimer: This tool is provided "as is" without warranty of any kind. Results are for educational and utility purposes.