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Flashcard Review Interval Calculator

Work out flashcard review interval instantly with clear inputs, formula shown and shareable results.

About Flashcard Review Interval Calculator

This follows the SM-2 rule: the ease factor is adjusted by 0.1 - (5 - q) x (0.08 + (5 - q) x 0.02), and the next interval is the current interval times the updated ease, or reset to one day if recall scored below 3. Spacing reviews just before forgetting is what makes flashcards efficient, and SM-2 automates that by letting each card's own difficulty set its schedule.

Formulas

Ease update

new ease = ease + 0.1 - (5 - quality) x (0.08 + (5 - quality) x 0.02), clamped to 1.3 - 3.0

Next interval

next interval = current interval x new ease, or 1 day when quality < 3

Worked example

With the default values below, Flashcard Review Interval Calculator returns Next review in of 8. Change any input above and every figure here is recalculated in your browser.

Inputs used

Current intervalminimum 1 days
3 days
Ease factoraccepts 1.3–3
2.5
Recall quality (0 blank - 5 perfect)accepts 0–5
4

Results

Next review in
8 days
Updated ease factor
2.500
Change in interval
166.7%
Outcome
Passed - interval extended

Step by step

  1. 1Values used
  2. 2Ease update
  3. 3Next interval
  4. 4Next review in= 8 days
  5. 5Updated ease factor= 2.500
  6. 6Change in interval= 166.7
  7. 7Outcome= Passed - interval extended

Assumptions and limits

  • The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is the Flashcard Review Interval figure worked out?

new ease = ease + 0.1 - (5 - quality) x (0.08 + (5 - quality) x 0.02), clamped to 1.3 - 3.0. This follows the SM-2 rule: the ease factor is adjusted by 0.1 - (5 - q) x (0.08 + (5 - q) x 0.02), and the next interval is the current interval times the updated ease, or reset to one day if recall scored below 3.

Why does this matter?

Spacing reviews just before forgetting is what makes flashcards efficient, and SM-2 automates that by letting each card's own difficulty set its schedule.

What do I need to enter?

Enter current interval, ease factor, recall quality (0 blank - 5 perfect). The defaults shown are a realistic worked example — swap in your own figures to get a result you can use.

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